intel: Don't call intelDestroyContext if there is no context to destroy

Some error paths in the device-specific context creation functions can exit
before the deintel_context structure is allocated.

NOTE: This is a candidate for the 9.0 branch.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=53618
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54301

src/mesa/drivers/dri/intel/intel_screen.c

@@ -821,7 +821,9 @@ intelCreateContext(gl_api api,
    if (success)
       return true;
 
-   intelDestroyContext(driContextPriv);
+   if (driContextPriv->driverPrivate != NULL)
+      intelDestroyContext(driContextPriv);
+
    return false;
 }