clang-format: Fix overloaded operator for global-scoped conversions.

Before:
  operator::A();

After:
  operator ::A();

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193605 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/Format/FormatTest.cpp b/unittests/Format/FormatTest.cpp
index cbac133..83035f7 100644
--- a/unittests/Format/FormatTest.cpp
+++ b/unittests/Format/FormatTest.cpp
@@ -3902,6 +3902,7 @@
 
   verifyGoogleFormat("operator void*();");
   verifyGoogleFormat("operator SomeType<SomeType<int>>();");
+  verifyGoogleFormat("operator ::A();");
 
   verifyFormat("using A::operator+;");
 }