Fix corner cases in PTH getSpelling() binary search.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@62187 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Lex/PTHLexer.cpp

@@ -400,6 +400,9 @@ unsigned PTHSpellingSearch::getSpellingBinarySearch(unsigned fpos,
     }
     
     if (TokOffset < fpos) {
+      if (i == min)
+        break;
+      
       min = i;
       continue;
     }