windows opengl: mpCurrentProgram seen as 0

in JunitTest_sc_unoapi_3.

Change-Id: Ibe12a31c1158f782bd7df115171b07e1843d025c
(cherry picked from commit 57fc41ad)
Reviewed-on: https://gerrit.libreoffice.org/18489Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>

vcl/source/opengl/OpenGLContext.cxx

@@ -1751,6 +1751,13 @@ OpenGLProgram* OpenGLContext::UseProgram( const OUString& rVertexShader, const O
         return pProgram;
 
     mpCurrentProgram = pProgram;
+
+    if (!mpCurrentProgram)
+    {
+        SAL_WARN("vcl.opengl", "OpenGLContext::UseProgram: mpCurrentProgram is 0");
+        return 0;
+    }
+
     mpCurrentProgram->Use();
 
     return mpCurrentProgram;