Replace double negation of !FileID.isInvalid() with FileID.isValid().
+couple more of double-negated !SourceLocation.isInvalid() unfixed in r249228.

llvm-svn: 249235
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index f410ad7..869890b 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -519,7 +519,7 @@
     llvm::MemoryBuffer::getMemBufferCopy(Predefines, "<built-in>");
   assert(SB && "Cannot create predefined source buffer");
   FileID FID = SourceMgr.createFileID(std::move(SB));
-  assert(!FID.isInvalid() && "Could not create FileID for predefines?");
+  assert(FID.isValid() && "Could not create FileID for predefines?");
   setPredefinesFileID(FID);
 
   // Start parsing the predefines.