[clang-format] Assert Line->First. NFC.

Cf. scan-build reports:
* https://llvm.org/reports/scan-build/report-AffectedRangeManager.cpp-nonPPLineAffected-34-16c04b.html#EndPath
* https://llvm.org/reports/scan-build/report-SortJavaScriptImports.cpp-parseModuleReferences-34-96a7f8.html#EndPath
* https://llvm.org/reports/scan-build/report-TokenAnnotator.cpp-setCommentLineLevels-26-77bdba.html#EndPath
* https://llvm.org/reports/scan-build/report-AffectedRangeManager.cpp-nonPPLineAffected-31-714434.html#EndPath
* https://llvm.org/reports/scan-build/report-TokenAnnotator.cpp-setCommentLineLevels-16-bd39d0.html#EndPath
* https://llvm.org/reports/scan-build/report-UnwrappedLineFormatter.cpp-format-90-668b2d.html#EndPath

clang/lib/Format/AffectedRangeManager.cpp

@@ -27,6 +27,7 @@ bool AffectedRangeManager::computeAffectedLines(
   const AnnotatedLine *PreviousLine = nullptr;
   while (I != E) {
     AnnotatedLine *Line = *I;
+    assert(Line->First);
     Line->LeadingEmptyLinesAffected = affectsLeadingEmptyLines(*Line->First);
 
     // If a line is part of a preprocessor directive, it needs to be formatted
@@ -113,6 +114,7 @@ bool AffectedRangeManager::nonPPLineAffected(
   // affected.
   bool SomeFirstChildAffected = false;
 
+  assert(Line->First);
   for (FormatToken *Tok = Line->First; Tok; Tok = Tok->Next) {
     // Determine whether 'Tok' was affected.
     if (affectsTokenRange(*Tok, *Tok, IncludeLeadingNewlines))

clang/lib/Format/SortJavaScriptImports.cpp

@@ -361,6 +361,7 @@ private:
     bool AnyImportAffected = false;
     bool FormattingOff = false;
     for (auto *Line : AnnotatedLines) {
+      assert(Line->First);
       Current = Line->First;
       LineEnd = Line->Last;
       // clang-format comments toggle formatting on/off.

clang/lib/Format/TokenAnnotator.cpp

@@ -2353,9 +2353,10 @@ private:
 void TokenAnnotator::setCommentLineLevels(
     SmallVectorImpl<AnnotatedLine *> &Lines) {
   const AnnotatedLine *NextNonCommentLine = nullptr;
-  for (AnnotatedLine *AL : llvm::reverse(Lines)) {
+  for (AnnotatedLine *Line : llvm::reverse(Lines)) {
+    assert(Line->First);
     bool CommentLine = true;
-    for (const FormatToken *Tok = AL->First; Tok; Tok = Tok->Next) {
+    for (const FormatToken *Tok = Line->First; Tok; Tok = Tok->Next) {
       if (!Tok->is(tok::comment)) {
         CommentLine = false;
         break;
@@ -2367,20 +2368,21 @@ void TokenAnnotator::setCommentLineLevels(
     if (NextNonCommentLine && CommentLine &&
         NextNonCommentLine->First->NewlinesBefore <= 1 &&
         NextNonCommentLine->First->OriginalColumn ==
-            AL->First->OriginalColumn) {
+            Line->First->OriginalColumn) {
       // Align comments for preprocessor lines with the # in column 0 if
       // preprocessor lines are not indented. Otherwise, align with the next
       // line.
-      AL->Level = (Style.IndentPPDirectives != FormatStyle::PPDIS_BeforeHash &&
-                   (NextNonCommentLine->Type == LT_PreprocessorDirective ||
-                    NextNonCommentLine->Type == LT_ImportStatement))
-                      ? 0
-                      : NextNonCommentLine->Level;
+      Line->Level =
+          (Style.IndentPPDirectives != FormatStyle::PPDIS_BeforeHash &&
+           (NextNonCommentLine->Type == LT_PreprocessorDirective ||
+            NextNonCommentLine->Type == LT_ImportStatement))
+              ? 0
+              : NextNonCommentLine->Level;
     } else {
-      NextNonCommentLine = AL->First->isNot(tok::r_brace) ? AL : nullptr;
+      NextNonCommentLine = Line->First->isNot(tok::r_brace) ? Line : nullptr;
     }
 
-    setCommentLineLevels(AL->Children);
+    setCommentLineLevels(Line->Children);
   }
 }
 

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -1213,6 +1213,7 @@ unsigned UnwrappedLineFormatter::format(
            Joiner.getNextMergedLine(DryRun, IndentTracker);
        Line; PrevPrevLine = PreviousLine, PreviousLine = Line, Line = NextLine,
                            FirstLine = false) {
+    assert(Line->First);
     const AnnotatedLine &TheLine = *Line;
     unsigned Indent = IndentTracker.getIndent();
 
@@ -1240,7 +1241,7 @@ unsigned UnwrappedLineFormatter::format(
 
     if (ShouldFormat && TheLine.Type != LT_Invalid) {
       if (!DryRun) {
-        bool LastLine = Line->First->is(tok::eof);
+        bool LastLine = TheLine.First->is(tok::eof);
         formatFirstToken(TheLine, PreviousLine, PrevPrevLine, Lines, Indent,
                          LastLine ? LastStartColumn : NextStartColumn + Indent);
       }