driDestroyDisplay: Remove Drivers list entry when dlclosing its handle.

This fixes a regression from commit f81b1dbe374fe446f6ef676e70a72952ffb47d4e:
Since then, driDestroyDisplay gets called from __glXFreeDisplayPrivate. It
dlcloses the handles associated with the display but fails to remove their
references from the Drivers list, so subsequent calls to OpenDriver return a
stale handle and an invalid createNewScreenFunc pointer. The attempt to call
the latter results in a segfault when running amoeba, e.g.

1 files changed, 18 insertions, 2 deletions

diff --git a/src/glx/x11/dri_glx.c b/src/glx/x11/dri_glx.c
index 0875361..5ff1a94 100644
--- a/src/glx/x11/dri_glx.c
+++ b/src/glx/x11/dri_glx.c
@@ -386,8 +386,24 @@ static void driDestroyDisplay(Display *dpy, void *private)
         const int numScreens = ScreenCount(dpy);
         int i;
         for (i = 0; i < numScreens; i++) {
-            if (pdpyp->libraryHandles[i])
-                dlclose(pdpyp->libraryHandles[i]);
+	   if (pdpyp->libraryHandles[i]) {
+	      __DRIdriver *driver, *prev;
+
+	      /* Remove driver from Drivers list */
+	      for (prev = NULL, driver = Drivers; driver;
+		   prev = driver, driver = driver->next) {
+		 if (driver->handle == pdpyp->libraryHandles[i]) {
+		    if (prev)
+		       prev->next = driver->next;
+		    else
+		       Drivers = driver->next;
+
+		    Xfree(driver);
+		 }
+	      }
+
+	      dlclose(pdpyp->libraryHandles[i]);
+	   }
         }
         Xfree(pdpyp->libraryHandles);
 	Xfree(pdpyp);