Fix a Malloc Checker FP by tracking return values from initWithCharacter

Fix a Malloc Checker FP by tracking return values from initWithCharacter
and other functions.

When these functions return null, the pointer is not freed by
them/ownership is not transfered. So we should allow the user to free
the pointer by calling another function when the return value is NULL.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@167813 91177308-0d34-0410-b5e6-96231b3b80d8