fix Swift runtime failure: arithmetic overflow

Author: eagleoflqj

macosfrontend/macosfrontend.swift

@@ -81,8 +81,7 @@ public func commitAndSetPreeditSync(
     // For SwiftUI TextField, there is a bug that if caret is at the end of text, zero-width space preedit
     // spreads from the start to the end, making the whole text underlined. Fortunately, SwiftUI's length
     // and selectedRange are reliable, so we use a normal space in this case.
-    if length > 0 && length - currentPreedit.count == selectedRange.location + selectedRange.length
-    {
+    if length > 0 && length - currentPreedit.count == NSMaxRange(selectedRange) {
       setPreedit(client, " ", 0)
     } else {
       setPreedit(client, zeroWidthSpace, 0)