Replace double-negated !SourceLocation.isInvalid() with SourceLocation.isValid().

llvm-svn: 249228
diff --git a/clang/lib/Frontend/TextDiagnostic.cpp b/clang/lib/Frontend/TextDiagnostic.cpp
index ee24c3b..d2dd192 100644
--- a/clang/lib/Frontend/TextDiagnostic.cpp
+++ b/clang/lib/Frontend/TextDiagnostic.cpp
@@ -1060,7 +1060,7 @@
     SmallVectorImpl<CharSourceRange>& Ranges,
     ArrayRef<FixItHint> Hints,
     const SourceManager &SM) {
-  assert(!Loc.isInvalid() && "must have a valid source location here");
+  assert(Loc.isValid() && "must have a valid source location here");
   assert(Loc.isFileID() && "must have a file location here");
 
   // If caret diagnostics are enabled and we have location, we want to