Fix missing unlock (reported by Coverity).

- Instead of just returning NULL, use the existing goto on_error to
handle the unlock and return NULL.

NB: Fixes Coverity CID1039383

Signed-off-by: Chris Michael <cp.michael@samsung.com>

src/lib/eet/eet_lib.c

@@ -1444,7 +1444,7 @@ eet_mmap(Eina_File *file)
 
    /* Allocate struct for eet file and have it zero'd out */
    ef = eet_file_malloc(1);
-   if (!ef) return NULL;
+   if (!ef) goto on_error;
 
    /* fill some of the members */
    INIT_FILE(ef);