[clang-format] Fix a crash in qualifier alignment

[owenpan]

Summary

Related to #54513.

[owenpan]

rG492cb7bf9164

clang/lib/Format/QualifierAlignmentFixer.cpp

if (Qual && Qual->is(QualifierType))
       break;
   }
 
   if (!Qual)
     return Tok;
 
   if (LastQual && Qual != LastQual && Qual->is(QualifierType)) {
     rotateTokens(SourceMgr, Fixes, Tok, Qual, /*Left=*/true);
+    if (!Qual->Next)
+      return Tok;
     Tok = Qual->Next;
   } else if (Tok->startsSequence(tok::identifier, QualifierType)) {
     if (Tok->Next->Next && Tok->Next->Next->isOneOf(tok::identifier, tok::star,
                                                     tok::amp, tok::ampamp)) {
       // Don't swap `::iterator const` to `::const iterator`.
       if (!Tok->Previous ||
           (Tok->Previous && !Tok->Previous->is(tok::coloncolon))) {
         rotateTokens(SourceMgr, Fixes, Tok, Tok->Next, /*Left=*/true);

clang/unittests/Format/QualifierFixerTest.cpp

TEST_F(QualifierFixerTest, NoOpQualifierReplacements) {
   FormatStyle Style = getLLVMStyle();
   Style.QualifierAlignment = FormatStyle::QAS_Custom;
   Style.QualifierOrder = {"static", "const", "type"};
 
   ReplacementCount = 0;
   EXPECT_EQ(ReplacementCount, 0);
   verifyFormat("static const uint32 foo[] = {0, 31};", Style);
   verifyFormat("#define MACRO static const", Style);
+  verifyFormat("using sc = static const", Style);
   EXPECT_EQ(ReplacementCount, 0);
 }
 
 TEST_F(QualifierFixerTest, QualifierTemplates) {
   FormatStyle Style = getLLVMStyle();
   Style.QualifierAlignment = FormatStyle::QAS_Custom;
   Style.QualifierOrder = {"static", "const", "type"};