Fix mouse picking

Currently, just treat mouse on the gap space to be on the row below it,
which is part of the cmdline. The alternative is to treat it as nothing,
but that leads to weird situations with the mouse cursor not being
reset. Just treat the row below it to have an extra tall hitbox.

Author: ychin

src/MacVim/MMCoreTextView.m

@@ -1115,15 +1115,35 @@ - (IBAction)selectAll:(id)sender
     [[self windowController] vimMenuItemAction:sender];
 }
 
+/// Converts a point in this NSView to a specific Vim row/column.
+///
+/// @param point The point in NSView. Note that it's y-up as that's Mac convention, whereas row starts from the top.
 - (BOOL)convertPoint:(NSPoint)point toRow:(int *)row column:(int *)column
 {
+    // Convert y-up to y-down.
     point.y = [self bounds].size.height - point.y;
 
     NSPoint origin = { insetSize.width, insetSize.height };
 
     if (!(cellSize.width > 0 && cellSize.height > 0))
         return NO;
 
+    if (alignCmdLineToBottom) {
+        // Account for the gap we added to pin cmdline to the bottom of the window
+        const NSRect frame = [self bounds];
+        const int insetBottom = [[NSUserDefaults standardUserDefaults] integerForKey:MMTextInsetBottomKey];
+        const CGFloat gapHeight = frame.size.height - grid.rows*cellSize.height - insetSize.height - insetBottom;
+        const CGFloat cmdlineRowY = insetSize.height + cmdlineRow*cellSize.height + 1;
+        if (point.y > cmdlineRowY) {
+            point.y -= gapHeight;
+            if (point.y <= cmdlineRowY) {
+                // This was inside the gap between top and bottom lines. Round it down
+                // to the next line.
+                point.y = cmdlineRowY + 1;
+            }
+        }
+    }
+
     if (row) *row = floor((point.y-origin.y-1) / cellSize.height);
     if (column) *column = floor((point.x-origin.x-1) / cellSize.width);