Ignore display bounds on resize-to-fit

The "resize to fit" feature (MOD+w or double-click on black borders)
computed the "optimal size" using the same function computing the
initial window size on start.

However, on "resize to fit", only the black borders must be removed (the
content size must be preserved), so the display bounds must not be
considered.

app/src/screen.c

@@ -90,7 +90,8 @@ is_optimal_size(struct sc_size current_size, struct sc_size content_size) {
 //  - it keeps the aspect ratio
 //  - it scales down to make it fit in the display_size
 static struct sc_size
-get_optimal_size(struct sc_size current_size, struct sc_size content_size) {
+get_optimal_size(struct sc_size current_size, struct sc_size content_size,
+                 bool within_display_bounds) {
     if (content_size.width == 0 || content_size.height == 0) {
         // avoid division by 0
         return current_size;
@@ -99,8 +100,9 @@ get_optimal_size(struct sc_size current_size, struct sc_size content_size) {
     struct sc_size window_size;
 
     struct sc_size display_size;
-    if (!get_preferred_display_bounds(&display_size)) {
-        // could not get display bounds, do not constraint the size
+    if (!within_display_bounds ||
+            !get_preferred_display_bounds(&display_size)) {
+        // do not constraint the size
         window_size = current_size;
     } else {
         window_size.width = MIN(current_size.width, display_size.width);
@@ -134,7 +136,7 @@ get_initial_optimal_size(struct sc_size content_size, uint16_t req_width,
                          uint16_t req_height) {
     struct sc_size window_size;
     if (!req_width && !req_height) {
-        window_size = get_optimal_size(content_size, content_size);
+        window_size = get_optimal_size(content_size, content_size, true);
     } else {
         if (req_width) {
             window_size.width = req_width;
@@ -559,7 +561,7 @@ resize_for_content(struct screen *screen, struct sc_size old_content_size,
         .height = (uint32_t) window_size.height * new_content_size.height
                 / old_content_size.height,
     };
-    target_size = get_optimal_size(target_size, new_content_size);
+    target_size = get_optimal_size(target_size, new_content_size, true);
     set_window_size(screen, target_size);
 }
 
@@ -694,7 +696,7 @@ screen_resize_to_fit(struct screen *screen) {
     struct sc_size window_size = get_window_size(screen);
 
     struct sc_size optimal_size =
-        get_optimal_size(window_size, screen->content_size);
+        get_optimal_size(window_size, screen->content_size, false);
 
     // Center the window related to the device screen
     assert(optimal_size.width <= window_size.width);