merge-ort: fix small memory leak in detect_and_process_renames()

merge-ort: fix small memory leak in detect_and_process_renames()

detect_and_process_renames() detects renames on both sides of history
and then combines these into a single diff_queue_struct.  The combined
diff_queue_struct needs to be able to hold the renames found on either
side, and since it knows the (maximum) size it needs, it pre-emptively
grows the array to the appropriate size:

	ALLOC_GROW(combined.queue,
		   renames->pairs[1].nr + renames->pairs[2].nr,
		   combined.alloc);

It then collects the items from each side:

	collect_renames(opt, &combined, MERGE_SIDE1, ...)
	collect_renames(opt, &combined, MERGE_SIDE2, ...)

Note, though, that collect_renames() sometimes determines that some
pairs are unnecessary and does not include them in the combined array.
When it is done, detect_and_process_renames() frees this memory:

	if (combined.nr) {
                ...
		free(combined.queue);
        }

The problem is that sometimes even when there are pairs, none of them
are necessary.  Instead of checking combined.nr, just remove the
if-check; free() knows to skip NULL pointers.  This change fixes the
following memory leak, as reported by valgrind:

==PID== 192 bytes in 1 blocks are definitely lost in loss record 107 of 134
==PID==    at 0xADDRESS: malloc
==PID==    by 0xADDRESS: realloc
==PID==    by 0xADDRESS: xrealloc (wrapper.c:126)
==PID==    by 0xADDRESS: detect_and_process_renames (merge-ort.c:3134)
==PID==    by 0xADDRESS: merge_ort_nonrecursive_internal (merge-ort.c:4610)
==PID==    by 0xADDRESS: merge_ort_internal (merge-ort.c:4709)
==PID==    by 0xADDRESS: merge_incore_recursive (merge-ort.c:4760)
==PID==    by 0xADDRESS: merge_ort_recursive (merge-ort-wrappers.c:57)
==PID==    by 0xADDRESS: try_merge_strategy (merge.c:753)
==PID==    by 0xADDRESS: cmd_merge (merge.c:1676)
==PID==    by 0xADDRESS: run_builtin (git.c:461)
==PID==    by 0xADDRESS: handle_builtin (git.c:713)
==PID==    by 0xADDRESS: run_argv (git.c:780)
==PID==    by 0xADDRESS: cmd_main (git.c:911)
==PID==    by 0xADDRESS: main (common-main.c:52)

Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>