library: move QUICK_THREADS hack before return

Minor complaint where a line to stop GCC from complaining occured
after the return.

proc/readproc.c

@@ -1114,10 +1114,10 @@ static proc_t* simple_readtask(PROCTAB *restrict const PT, const proc_t *restric
 
     return t;
 next_task:
-    return NULL;
 #ifndef QUICK_THREADS
     (void)p;
 #endif
+    return NULL;
 }
 
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