tmux: Fix edge cases in paragraph text-object

Also add comments explaining the history & pane position checks in the
C-y and C-e bindings, since I used those and had to rethink about what
they're doing.

.config/tmux/tmux.conf

@@ -176,11 +176,19 @@ bind -T copy-mode-vi i \
 			}{ if -F "#{==:%1,p}" {
 				# send "{j0o}k$"
 				send -X previous-paragraph
-				send -X cursor-down
+				# don't move down if we're at the very first
+				# paragraph
+				if -F "#{||:#{e|<:#{scroll_position},#{history_size}},#{e|>:#{copy_cursor_y},#{scroll_region_upper}}}" {
+					send -X cursor-down
+				}
 				send -X start-of-line
 				send -X other-end
 				send -X next-paragraph
-				send -X cursor-up
+				# don't move up if we're at the very last
+				# paragraph
+				if -F "#{||:#{e|>:#{scroll_position},0},#{e|<:#{copy_cursor_y},#{scroll_region_lower}}}" {
+					send -X cursor-up
+				}
 				send -X end-of-line
 			}{ if -F '#{==:%1,"}' {
 				send -X jump-to-backward '"'
@@ -201,16 +209,20 @@ bind -T copy-mode-vi i \
 # scrolling when the respective line is visible. This mimics the behaviour of
 # vim's C-y at the top of the file.
 bind -T copy-mode-vi C-e \
+	# check that there is still history beneath to scroll to.
 	if -F "#{e|>:#{scroll_position},0}" {
 		send-keys -X scroll-down
+		# check that the cursor is not at the top of the pane
 		if -F "#{e|>:#{copy_cursor_y},#{scroll_region_upper}}" {
 			send-keys -X cursor-up
 		}
 	}
 
 bind -T copy-mode-vi C-y \
+	# check that there is still history above to scroll to.
 	if -F "#{e|<:#{scroll_position},#{history_size}}" {
 		send-keys -X scroll-up
+		# check that the cursor is not at the bottom of the pane
 		if -F "#{e|<:#{copy_cursor_y},#{scroll_region_lower}}" {
 			send-keys -X cursor-down
 		}