FunctionTypeLocs don't necessarily provide ParmVarDecls, so don't crash if
one was PCH'ed without any.

llvm-svn: 84920
diff --git a/clang/lib/Frontend/PCHReader.cpp b/clang/lib/Frontend/PCHReader.cpp
index 7dc60f8..e804bfc 100644
--- a/clang/lib/Frontend/PCHReader.cpp
+++ b/clang/lib/Frontend/PCHReader.cpp
@@ -2065,7 +2065,7 @@
   TL.setLParenLoc(SourceLocation::getFromRawEncoding(Record[Idx++]));
   TL.setRParenLoc(SourceLocation::getFromRawEncoding(Record[Idx++]));
   for (unsigned i = 0, e = TL.getNumArgs(); i != e; ++i) {
-    TL.setArg(i, cast<ParmVarDecl>(Reader.GetDecl(Record[Idx++])));
+    TL.setArg(i, cast_or_null<ParmVarDecl>(Reader.GetDecl(Record[Idx++])));
   }
 }
 void TypeLocReader::VisitFunctionProtoTypeLoc(FunctionProtoTypeLoc TL) {