Fixed shader and program cleanup.

src/renderer_gl.cpp

@@ -1071,8 +1071,12 @@ namespace bgfx
 		}
 		m_numPredefined = 0;
 
-		GL_CHECK(glUseProgram(0) );
-		GL_CHECK(glDeleteProgram(m_id) );
+		if (0 != m_id)
+		{
+			GL_CHECK(glUseProgram(0) );
+			GL_CHECK(glDeleteProgram(m_id) );
+			m_id = 0;
+		}
 
 		m_vcref.invalidate(s_renderCtx->m_vaoStateCache);
 	}

src/renderer_gl.h

@@ -583,6 +583,11 @@ namespace bgfx
 
 	struct Shader
 	{
+		Shader()
+			: m_id(0)
+		{
+		}
+
 		void create(GLenum _type, Memory* _mem)
 		{
 			m_id = glCreateShader(_type);
@@ -622,7 +627,11 @@ namespace bgfx
 
 		void destroy()
 		{
-			GL_CHECK(glDeleteShader(m_id) );
+			if (0 != m_id)
+			{
+				GL_CHECK(glDeleteShader(m_id) );
+				m_id = 0;
+			}
 		}
 
 		GLuint m_id;
@@ -657,7 +666,8 @@ namespace bgfx
 	struct Program
 	{
 		Program()
-			: m_constantBuffer(NULL)
+			: m_id(0)
+			, m_constantBuffer(NULL)
 			, m_numPredefined(0)
 		{
 		}