user32/edit: Avoid division by zero in EDIT_EM_LineScroll_internal.

dlls/user32/edit.c

@@ -1674,8 +1674,12 @@ static BOOL EDIT_EM_LineScroll_internal(EDITSTATE *es, INT dx, INT dy)
 {
 	INT nyoff;
 	INT x_offset_in_pixels;
-	INT lines_per_page = (es->format_rect.bottom - es->format_rect.top) /
-			      es->line_height;
+	INT lines_per_page;
+
+	if (!es->line_height || !es->char_width)
+		return TRUE;
+
+	lines_per_page = (es->format_rect.bottom - es->format_rect.top) / es->line_height;
 
 	if (es->style & ES_MULTILINE)
 	{

dlls/user32/tests/edit.c

@@ -1765,6 +1765,8 @@ static LRESULT CALLBACK test_class_proc(HWND hwnd, UINT message, WPARAM wParam,
             ok(r == 1, "Returned %ld, expected 1.\n", r);
             r = SendMessageA(hwnd, WM_SIZE, 0, 0x00100010);
             todo_wine ok(r == 1, "Returned %ld, expected 1.\n", r);
+            r = SendMessageA(hwnd, EM_LINESCROLL, 1, 1);
+            ok(r == 1, "Returned %ld, expected 1.\n", r);
 
             return result;
 
@@ -1775,6 +1777,8 @@ static LRESULT CALLBACK test_class_proc(HWND hwnd, UINT message, WPARAM wParam,
             ok(r == 1, "Returned %ld, expected 1.\n", r);
             r = SendMessageA(hwnd, WM_SIZE, 0, 0x00100010);
             todo_wine ok(r == 1, "Returned %ld, expected 1.\n", r);
+            r = SendMessageA(hwnd, EM_LINESCROLL, 1, 1);
+            ok(r == 1, "Returned %ld, expected 1.\n", r);
 
             break;
     }