mandelbrot: added return statements to void* functions"

mandelbrot/mandelbrot.c

@@ -70,6 +70,7 @@ void *produce(void *b)
 			enqueue(buf->q, m, buf->lock);
 		}
 	}
+	return NULL;
 }
 
 void *consume(void *b)
@@ -97,6 +98,7 @@ void *consume(void *b)
 			i++;
 		}
 	}
+	return NULL;
 }
 
 int main(int argc, char **argv)