Update catalog.c - Removing sanity check as there is no need of checking non null pointer (#31653)

There is no need to check the pointer as the pointer will never be NULL.

Co-authored-by: Frantisek Sumsal <frantisek@sumsal.cz>

src/libsystemd/sd-journal/catalog.c

@@ -618,8 +618,7 @@ int catalog_get(const char* database, sd_id128_t id, char **_text) {
         r = 0;
 
 finish:
-        if (p)
-                munmap(p, st.st_size);
+        (void) munmap(p, st.st_size);
 
         return r;
 }