terminal: Handle selection for pointer positions outside widget correctly

That is, don't crash and select entire first/last line when the pointer
is above or below widget.

clients/terminal.c

@@ -2279,8 +2279,9 @@ recompute_selection(struct terminal *terminal)
 	side_margin = allocation.x + (allocation.width - width) / 2;
 	top_margin = allocation.y + (allocation.height - height) / 2;
 
-	start_row = (terminal->selection_start_y - top_margin) / ch;
-	end_row = (terminal->selection_end_y - top_margin) / ch;
+	start_row = (terminal->selection_start_y - top_margin + ch) / ch - 1;
+	end_row = (terminal->selection_end_y - top_margin + ch) / ch - 1;
+
 	if (start_row < end_row ||
 	    (start_row == end_row &&
 	     terminal->selection_start_x < terminal->selection_end_x)) {
@@ -2295,8 +2296,13 @@ recompute_selection(struct terminal *terminal)
 		end_x = terminal->selection_start_x;
 	}
 
+	if (terminal->selection_start_row < 0) {
+		terminal->selection_start_row = 0;
+		terminal->selection_start_col = 0;
+	} else {
 		x = side_margin + cw / 2;
-	data = terminal_get_row(terminal, terminal->selection_start_row);
+		data = terminal_get_row(terminal,
+					terminal->selection_start_row);
 		word_start = 0;
 		for (col = 0; col < terminal->width; col++, x += cw) {
 			if (col == 0 || wordsep(data[col - 1].ch))
@@ -2316,7 +2322,12 @@ recompute_selection(struct terminal *terminal)
 			terminal->selection_start_col = col;
 			break;
 		}
+	}
 
+	if (terminal->selection_end_row >= terminal->height) {
+		terminal->selection_end_row = terminal->height;
+		terminal->selection_end_col = 0;
+	} else {
 		x = side_margin + cw / 2;
 		data = terminal_get_row(terminal, terminal->selection_end_row);
 		for (col = 0; col < terminal->width; col++, x += cw) {
@@ -2328,6 +2339,7 @@ recompute_selection(struct terminal *terminal)
 		}
 
 		terminal->selection_end_col = col;
+	}
 
 	return 1;
 }