Fix another occurrence of inverted logic on the result of MappedFile::map

llvm-svn: 29828
diff --git a/llvm/lib/Debugger/SourceFile.cpp b/llvm/lib/Debugger/SourceFile.cpp
index 799231f..ebea307 100644
--- a/llvm/lib/Debugger/SourceFile.cpp
+++ b/llvm/lib/Debugger/SourceFile.cpp
@@ -20,7 +20,7 @@
 ///
 void SourceFile::readFile() {
   std::string ErrMsg;
-  if (File.map(&ErrMsg))
+  if (!File.map(&ErrMsg))
     throw ErrMsg;
 }