do not check for NULL in FREE macro

free(3) is safe to invoke on a NULL pointer, in which case no action is
taken. This change adjusts the FREE macros to omit this unnecessary
check.

i3bar/include/util.h

@@ -20,12 +20,10 @@
 #define STARTS_WITH(string, len, needle) (((len) >= strlen((needle))) && strncasecmp((string), (needle), strlen((needle))) == 0)
 
 /* Securely free p */
-#define FREE(p)          \
-    do {                 \
-        if (p != NULL) { \
-            free(p);     \
-            p = NULL;    \
-        }                \
+#define FREE(p)   \
+    do {          \
+        free(p);  \
+        p = NULL; \
     } while (0)
 
 /* Securely free single-linked list */