Try to fix linux compilation.

src/graphics/shader.hpp

@@ -94,6 +94,11 @@ public:
     // ------------------------------------------------------------------------
     /** Activates the shader calling glUseProgram. */
     void use() { glUseProgram(m_program); }
+    // ------------------------------------------------------------------------
+    GLuint getUniformLocation(const char *name)
+    {
+        return glGetUniformLocation(m_program, name);
+    }   // getUniformLocation
 };   // ShaderBase
 
 // ============================================================================

src/graphics/texture_shader.hpp

@@ -122,7 +122,7 @@ private:
         assert(sampler_type >= ST_MIN && sampler_type <= ST_MAX);
         m_texture_type.push_back(m_all_texture_types[sampler_type]);
 
-        GLuint location = glGetUniformLocation(m_program, name);
+        GLuint location = getUniformLocation(name);
         m_texture_location.push_back(location);
         glUniform1i(location, tex_unit);
         m_texture_units.push_back(tex_unit);