Fix: Unlock the heap mutex before runing sys_alloc.

test.c

@@ -82,13 +82,13 @@ void *custom_malloc(heap_t* heap, size_t size) {
 		}
 
 		if(!found) {
+			posix_unlock(heap);
 			return sys_alloc(size);
 		}
 
 	}
 
 	posix_unlock(heap);
-
 	return ptr;
 }