cocoa: clamp mouse position to window.

Prevents out-of-window coordinates being reported for mouse coordinates.
Previously they could be out-of-window coordinates on init or on resize.

(cherry picked from commit 39537f6474)

video/out/cocoa/events_view.m

@@ -206,6 +206,8 @@
 - (void)signalMousePosition
 {
     NSPoint p = [self convertPointToPixels:[self mouseLocation]];
+    p.x = MIN(MAX(p.x, 0), self.bounds.size.width-1);
+    p.y = MIN(MAX(p.y, 0), self.bounds.size.height-1);
     [self.adapter signalMouseMovement:p];
 }