[clang-format] Stop crashing when formatting Verilog (#112043)

The part of the code for parsing Verilog module instantiations
dereferenced a pointer without checking for null pointer. The pointer
may be null if the input is not complete and a line starts with a comma.

Author: sstwcw

clang/lib/Format/TokenAnnotator.cpp

@@ -1551,7 +1551,8 @@ class AnnotatingParser {
           // Case D.
           if (Keywords.isVerilogIdentifier(*Prev) && PrevPrev->is(tok::comma)) {
             const FormatToken *PrevParen = PrevPrev->getPreviousNonComment();
-            if (PrevParen->is(tok::r_paren) && PrevParen->MatchingParen &&
+            if (PrevParen && PrevParen->is(tok::r_paren) &&
+                PrevParen->MatchingParen &&
                 PrevParen->MatchingParen->is(TT_VerilogInstancePortLParen)) {
               return true;
             }

clang/unittests/Format/FormatTestVerilog.cpp

@@ -964,6 +964,7 @@ TEST_F(FormatTestVerilog, Instantiation) {
                "        .qbar(out1),\n"
                "        .clear(in1),\n"
                "        .preset(in2));");
+  verifyNoCrash(", ff1();");
   // With breaking between instance ports disabled.
   auto Style = getDefaultStyle();
   Style.VerilogBreakBetweenInstancePorts = false;