Revert "glx: Initialize glx even if there are currently no screens attached"

This wasn't intended to be present in the merged patch series.  Sorry for the noise.

This reverts commit 7e7480ff47.

glx/glxext.c

@@ -320,6 +320,23 @@ GlxPushProvider(__GLXprovider * provider)
     __glXProviderStack = provider;
 }
 
+static Bool
+checkScreenVisuals(void)
+{
+    int i, j;
+
+    for (i = 0; i < screenInfo.numScreens; i++) {
+        ScreenPtr screen = screenInfo.screens[i];
+        for (j = 0; j < screen->numVisuals; j++) {
+            if (screen->visuals[j].class == TrueColor ||
+                screen->visuals[j].class == DirectColor)
+                return True;
+        }
+    }
+
+    return False;
+}
+
 /*
 ** Initialize the GLX extension.
 */
@@ -338,6 +355,10 @@ GlxExtensionInit(void)
         *stack = &__glXDRISWRastProvider;
     }
 
+    /* Mesa requires at least one True/DirectColor visual */
+    if (!checkScreenVisuals())
+        return;
+
     __glXContextRes = CreateNewResourceType((DeleteType) ContextGone,
                                             "GLXContext");
     __glXDrawableRes = CreateNewResourceType((DeleteType) DrawableGone,