combine-diff.c: type sanity.
combine-diff.c: type sanity.

In diff_tree_combined(), show_log_first boolean is initialized with
rev->loginfo (pointer to a string); the intention is that if we have
some string to be emitted we would want to remember that fact.  Picky
compilers are offended by this, so make the expression a bit type-safer.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git