SDL: cocoa: Report an error if SDL_SetClipboardText() isn't using UTF-8 encoding.

SDL Commits
1 
From 9dc97afa7190aca5bdf923ed13d723197c083547 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Sat, 8 May 2021 12:39:50 -0400
Subject: [PATCH] cocoa: Report an error if SDL_SetClipboardText() isn't using
 UTF-8 encoding.

Fixes #4110.
---
 src/video/cocoa/SDL_cocoaclipboard.m | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/video/cocoa/SDL_cocoaclipboard.m b/src/video/cocoa/SDL_cocoaclipboard.m
index a091d8feb..bfd35f055 100644
--- a/src/video/cocoa/SDL_cocoaclipboard.m
+++ b/src/video/cocoa/SDL_cocoaclipboard.m
@@ -32,10 +32,14 @@
     SDL_VideoData *data = (SDL_VideoData *) _this->driverdata;
     NSPasteboard *pasteboard;
     NSString *format = NSPasteboardTypeString;
+    NSString *nsstr = [NSString stringWithUTF8String:text];
+    if (nsstr == nil) {
+        return SDL_SetError("Couldn't create NSString; is your string data in UTF-8 format?");
+    }
 
     pasteboard = [NSPasteboard generalPasteboard];
     data->clipboard_count = [pasteboard declareTypes:[NSArray arrayWithObject:format] owner:nil];
-    [pasteboard setString:[NSString stringWithUTF8String:text] forType:format];
+    [pasteboard setString:nsstr forType:format];
 
     return 0;
 }}
@@ -61,7 +65,7 @@
         } else {
             utf8 = [string UTF8String];
         }
-        text = SDL_strdup(utf8);
+        text = SDL_strdup(utf8 ? utf8 : "");
     } else {
         text = SDL_strdup("");
     }