Prevent workspace gaps from ending up negative

Since outer gaps can be negative we need to robustly prevent the
resulting gaps from ending up negative. The previous code only did this
on workspace creation but the gaps can change after that.

Fixes #4304

sway/tree/workspace.c

@@ -54,21 +54,6 @@ struct sway_output *workspace_get_initial_output(const char *name) {
 	return root->outputs->length ? root->outputs->items[0] : root->noop_output;
 }
 
-static void prevent_invalid_outer_gaps(struct sway_workspace *ws) {
-	if (ws->gaps_outer.top < -ws->gaps_inner) {
-		ws->gaps_outer.top = -ws->gaps_inner;
-	}
-	if (ws->gaps_outer.right < -ws->gaps_inner) {
-		ws->gaps_outer.right = -ws->gaps_inner;
-	}
-	if (ws->gaps_outer.bottom < -ws->gaps_inner) {
-		ws->gaps_outer.bottom = -ws->gaps_inner;
-	}
-	if (ws->gaps_outer.left < -ws->gaps_inner) {
-		ws->gaps_outer.left = -ws->gaps_inner;
-	}
-}
-
 struct sway_workspace *workspace_create(struct sway_output *output,
 		const char *name) {
 	if (output == NULL) {
@@ -111,9 +96,6 @@ struct sway_workspace *workspace_create(struct sway_output *output,
 			if (wsc->gaps_inner != INT_MIN) {
 				ws->gaps_inner = wsc->gaps_inner;
 			}
-			// Since default outer gaps can be smaller than the negation of
-			// workspace specific inner gaps, check outer gaps again
-			prevent_invalid_outer_gaps(ws);
 
 			// Add output priorities
 			for (int i = 0; i < wsc->outputs->length; ++i) {
@@ -759,6 +741,14 @@ void workspace_add_gaps(struct sway_workspace *ws) {
 		ws->current_gaps.bottom += gaps_vertical1;
 	}
 
+	// Prevent the resulting gaps from turning out negative, since outer gaps can
+	// be negative and nothing ensures they will not be larger than the current
+	// inner gaps.
+	ws->current_gaps.left = MAX(0, ws->current_gaps.left);
+	ws->current_gaps.right = MAX(0, ws->current_gaps.right);
+	ws->current_gaps.top = MAX(0, ws->current_gaps.top);
+	ws->current_gaps.bottom = MAX(0, ws->current_gaps.bottom);
+
 	// Now that we have the total gaps calculated we may need to clamp them in
 	// case they've made the available area too small
 	if (ws->width - ws->current_gaps.left - ws->current_gaps.right < MIN_SANE_W &&