Added missing statement with sfShader_createFromX

We can now call sfShader_createFromFile/Memory/Stream with only a
geometry file/memory/stream.

src/SFML/Graphics/Shader.cpp

@@ -59,11 +59,19 @@ sfShader* sfShader_createFromFile(const char* vertexShaderFilename, const char*
             }
         }
         else
+        {
+            if (!vertexShaderFilename && !fragmentShaderFilename)
+            {
+                // geometry shader only
+                success = shader->This.loadFromFile(geometryShaderFilename, sf::Shader::Geometry);
+            }
+            else
             {
                 // vertex + geometry + fragment shaders
                 success = shader->This.loadFromFile(vertexShaderFilename, geometryShaderFilename, fragmentShaderFilename);
             }
         }
+    }
 
     if (!success)
     {
@@ -101,11 +109,19 @@ sfShader* sfShader_createFromMemory(const char* vertexShader, const char* geomet
             }
         }
         else
+        {
+            if (!vertexShader && !fragmentShader)
+            {
+                // geometry shader only
+                success = shader->This.loadFromMemory(geometryShader, sf::Shader::Geometry);
+            }
+            else
             {
                 // vertex + geometry + fragment shaders
                 success = shader->This.loadFromMemory(vertexShader, geometryShader, fragmentShader);
             }
         }
+    }
 
     if (!success)
     {
@@ -147,14 +163,22 @@ sfShader* sfShader_createFromStream(sfInputStream* vertexShaderStream, sfInputSt
             }
         }
         else
+        {
+            CallbackStream geometryStream(geometryShaderStream);
+            if (!vertexShaderStream && !fragmentShaderStream)
+            {
+                // geometry shader only
+                success = shader->This.loadFromStream(geometryStream, sf::Shader::Geometry);
+            }
+            else
             {
                 // vertex + geometry + fragment shaders
                 CallbackStream vertexStream(vertexShaderStream);
-            CallbackStream geometryStream(geometryShaderStream);
                 CallbackStream fragmentStream(fragmentShaderStream);
                 success = shader->This.loadFromStream(vertexStream, geometryStream, fragmentStream);
             }
         }
+    }
 
     if (!success)
     {