Fix a few coverity complaints

All minor:
- execdir does not need initialization, it's not used until written to
- 'newest' could be NULL
- zalloc(-1) confuses coverity
- 't' is never used in that test

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit cfd8e6c76c)

src/builddir.h

@@ -35,7 +35,7 @@
 static inline char *
 builddir_lookup(void)
 {
-	char execdir[PATH_MAX] = {0};
+	char execdir[PATH_MAX];
 	char *pathsep;
 	ssize_t nread;
 

src/evdev-mt-touchpad-thumb.c

@@ -358,7 +358,8 @@ tp_thumb_update_multifinger(struct tp_dispatch *tp)
 	 * the behavior of the other touches.)
 	 */
 
-	if ((newest->initial_time - oldest->initial_time) < THUMB_TIMEOUT &&
+	if (newest &&
+	    (newest->initial_time - oldest->initial_time) < THUMB_TIMEOUT &&
 	    first->point.y < tp->thumb.lower_thumb_line) {
 		tp_thumb_lift(tp);
 		return;

test/litest-selftest.c

@@ -350,7 +350,7 @@ END_TEST
 
 START_TEST(zalloc_overflow)
 {
-	zalloc(-1);
+	zalloc((size_t)-1);
 }
 END_TEST