[MP] fix off-by-one in TruncateGLExtensionsString which affects mods …

…not derived from OJK (#1175)

UI_DrawGLInfo has an array of size 128, which was being filled from a GL extensions string of 129 words and displaying garbage in the UI.
Ref #472

codemp/rd-vanilla/tr_init.cpp

@@ -751,7 +751,7 @@ static const char *TruncateGLExtensionsString (const char *extensionsString, int
 
 	char *truncatedExtensions;
 
-	while ( (q = strchr (p, ' ')) != NULL && numExtensions <= maxExtensions )
+	while ( (q = strchr (p, ' ')) != NULL && numExtensions < maxExtensions )
 	{
 		p = q + 1;
 		numExtensions++;