tests/ui: omit the red square from screenshots

except the first one on homescreen because it gets rendered only once

core/src/apps/debug/__init__.py

@@ -37,9 +37,11 @@ if __debug__:
     layout_change_chan = loop.chan()
     current_content = None  # type: Optional[List[str]]
 
-    def screenshot() -> None:
+    def screenshot() -> bool:
         if utils.SAVE_SCREEN or save_screen:
             ui.display.save(save_screen_directory + "/refresh-")
+            return True
+        return False
 
     def notify_layout_change(layout: ui.Layout) -> None:
         global current_content

core/src/trezor/ui/__init__.py

@@ -42,9 +42,9 @@ if __debug__:
     from apps.debug import screenshot
 
     def refresh() -> None:
+        if not screenshot():
             display.bar(Display.WIDTH - 8, 0, 8, 8, 0xF800)
         display.refresh()
-        screenshot()
 
 
 else: