glx: Add isDirect back to __GLXcontextRec. It is needed

to check whether oldGC is used for direct rendering in
function MakeContextCurrent. However it is possible
oldGC->driContext is already freed. fix bug #14926.

src/glx/x11/glxclient.h

@@ -309,6 +309,11 @@ struct __GLXcontextRec {
      */
     GLenum error;
 
+    /**
+     * Whether this context does direct rendering.
+     */
+    Bool isDirect;
+
     /**
      * \c dpy of current display for this context.  Will be \c NULL if not
      * current to any display, or if this is the "dummy context".

src/glx/x11/glxcmds.c

@@ -313,6 +313,7 @@ GLXContext AllocateGLXContext( Display *dpy )
     gc->fillImage = __glFillImage;
     gc->pc = gc->buf;
     gc->bufEnd = gc->buf + bufSize;
+    gc->isDirect = GL_FALSE;
     if (__glXDebug) {
 	/*
 	** Set limit register so that there will be one command per packet
@@ -404,6 +405,7 @@ CreateContext(Display *dpy, XVisualInfo *vis,
 		gc->screen = mode->screen;
 		gc->psc = psc;
 		gc->mode = mode;
+		gc->isDirect = GL_TRUE;
 	    }
 	}
 #endif

src/glx/x11/glxext.c

@@ -1256,7 +1256,7 @@ static Bool MakeContextCurrent(Display *dpy, GLXDrawable draw,
 	/* Send a glXMakeCurrent request to bind the new context. */
 	bindReturnValue = 
 	  SendMakeCurrentRequest(dpy, opcode, gc ? gc->xid : None,
-				 ((dpy != oldGC->currentDpy) || oldGC->driContext)
+				 ((dpy != oldGC->currentDpy) || oldGC->isDirect)
 				 ? None : oldGC->currentContextTag,
 				 draw, read, &reply);
     }
@@ -1267,7 +1267,7 @@ static Bool MakeContextCurrent(Display *dpy, GLXDrawable draw,
     }
 
     if ((dpy != oldGC->currentDpy || (gc && gc->driContext)) &&
-	!oldGC->driContext && oldGC != &dummyContext) {
+	!oldGC->isDirect && oldGC != &dummyContext) {
 	xGLXMakeCurrentReply dummy_reply;
 
 	/* We are either switching from one dpy to another and have to