sdl12-compat: SDL_EnableUNICODE(-1) should query the current state without changing it.

SDL Commits
1 
From c39259cc9cd2d44321a188035dc613f1a13a1c6c Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Thu, 17 Jun 2021 21:29:24 -0400
Subject: [PATCH] SDL_EnableUNICODE(-1) should query the current state without
 changing it.

---
 src/SDL12_compat.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index 8734e7d..da5e61d 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -5488,12 +5488,14 @@ SDL_GetKeyRepeat(int *delay, int *interval)
 DECLSPEC int SDLCALL
 SDL_EnableUNICODE(int enable)
 {
-    int old = EnabledUnicode;
-    EnabledUnicode = enable;
-    if (enable) {
-        SDL20_StartTextInput();
-    } else {
-        SDL20_StopTextInput();
+    const int old = EnabledUnicode;
+    if (enable >= 0) {
+        EnabledUnicode = enable;
+        if (enable) {
+            SDL20_StartTextInput();
+        } else {
+            SDL20_StopTextInput();
+        }
     }
     return old;
 }