Fix crash when dumping NamedDecl with NULL getQualifier().

[dawn]

Summary

This fixes calls to the dump() routine for cases when the NamedDecl's getQualifier() is NULL.

Since ASTDumper is a debugging utility, it should handle the case that getQualifier() is NULL. I don't know if the crash can happen in clang, but it can happen while debugging lldb for the source:

namespace ns {
    int func();
    int context() {
        // execution context is here
    }
}

commands in lldb being debugged:

p ns::func() <- adds the namespace to decl map in lldb
p func()  <- crash while dumping the NamedDecl of the function's parent's
             declaration contexts because getQualifier() is NULL.

[aaron.ballman]

LGTM, thank you!

cfe/trunk/lib/AST/ASTDumper.cpp

void ASTDumper::VisitTemplateTemplateParmDecl(
   dumpName(D);
   dumpTemplateParameters(D->getTemplateParameters());
   if (D->hasDefaultArgument())
     dumpTemplateArgumentLoc(D->getDefaultArgument());
 }
 
 void ASTDumper::VisitUsingDecl(const UsingDecl *D) {
   OS << ' ';
+  if (D->getQualifier())
     D->getQualifier()->print(OS, D->getASTContext().getPrintingPolicy());
   OS << D->getNameAsString();
 }
 
 void ASTDumper::VisitUnresolvedUsingTypenameDecl(
     const UnresolvedUsingTypenameDecl *D) {
   OS << ' ';
+  if (D->getQualifier())
     D->getQualifier()->print(OS, D->getASTContext().getPrintingPolicy());
   OS << D->getNameAsString();
 }
 
 void ASTDumper::VisitUnresolvedUsingValueDecl(const UnresolvedUsingValueDecl *D) {
   OS << ' ';
+  if (D->getQualifier())
     D->getQualifier()->print(OS, D->getASTContext().getPrintingPolicy());
   OS << D->getNameAsString();
   dumpType(D->getType());
 }
 
 void ASTDumper::VisitUsingShadowDecl(const UsingShadowDecl *D) {
   OS << ' ';
   dumpBareDeclRef(D->getTargetDecl());
 }