Ensure that grab regions are valid

Author: jholveck

src/mss/base.py

@@ -112,6 +112,13 @@ def grab(self, monitor: Monitor | tuple[int, int, int, int], /) -> ScreenShot:
                 "height": monitor[3] - monitor[1],
             }
 
+        if monitor["left"] < 0 or monitor["top"] < 0:
+            msg = f"Region has negative coordinates: {monitor!r}"
+            raise ScreenShotError(msg)
+        if monitor["width"] <= 0 or monitor["height"] <= 0:
+            msg = f"Region has zero or negative size: {monitor!r}"
+            raise ScreenShotError(msg)
+
         with lock:
             screenshot = self._grab_impl(monitor)
             if self.with_cursor and (cursor := self._cursor_impl()):