Prevent errant scroll on mouse click (Bug#31546)

* src/nsterm.m (ns_mouse_position): Use correct frame when determining
  mouse position.
* lisp/mouse.el (mouse-drag-track): Only account for mode-line height
  if `mode-line-format' is non-nil.

lisp/mouse.el

@@ -1225,7 +1225,11 @@ The region will be defined with mark and point."
 	 (bounds (window-edges start-window))
 	 (make-cursor-line-fully-visible nil)
 	 (top (nth 1 bounds))
-	 (bottom (if (window-minibuffer-p start-window)
+	 (bottom (if (or (window-minibuffer-p start-window)
+                         ;; Do not account for the mode line if there
+                         ;; is no mode line, which is common for child
+                         ;; frames.
+                         (not mode-line-format))
 		     (nth 3 bounds)
 		   ;; Don't count the mode line.
 		   (1- (nth 3 bounds))))

src/nsterm.m

@@ -2547,7 +2547,7 @@ so some key presses (TAB) are swallowed by the system. */
 
   if (f && FRAME_NS_P (f))
     {
-      view = FRAME_NS_VIEW (*fp);
+      view = FRAME_NS_VIEW (f);
 
       position = [[view window] mouseLocationOutsideOfEventStream];
       position = [view convertPoint: position fromView: nil];