[analyzer] Fix a crash in plist-html generation introduced in r162939.

Basically, do the correct thing to fix the XML generation error, rather
than making it even worse by unilaterally dereferencing a null pointer.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162964 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed