Add missing null pointer check in -ftime-trace code

createOutputFile diagnoses the error for the caller already, so recover
by not writing the output.

Fixes PR43555

No test, since I couldn't think of a good, portable, simple way to make
the regular -o output file writable, but outputfile.json not writable.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@373771 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed