UPBGE: Fix KX_Mesh.transformUV with invalid UV layer.

This function can copy an uv layer to an other, but no check was proceeded
for the source layer and created invalid memory access.

To solve this issue and simplify the error checking for uv layers, the function
uvExist is created as adviced by youle. This function check if the layer passed
is between 0 and format.uvSize.

Fix issue: #955.

source/gameengine/Ketsji/KX_Mesh.cpp

@@ -275,6 +275,11 @@ PyObject *KX_Mesh::PyTransform(PyObject *args, PyObject *kwds)
 	Py_RETURN_NONE;
 }
 
+static bool uvExist(short index, const RAS_DisplayArray::Format& format)
+{
+	return (0 <= index && index < format.uvSize);
+}
+
 PyObject *KX_Mesh::PyTransformUV(PyObject *args, PyObject *kwds)
 {
 	int matindex;
@@ -321,20 +326,23 @@ PyObject *KX_Mesh::PyTransformUV(PyObject *args, PyObject *kwds)
 		ok = true;
 
 		for (unsigned int j = 0, size = array->GetVertexCount(); j < size; ++j) {
-			if (uvindex_from != -1) {
+			// Copy one layer (optional).
+			if (uvindex_from != -1 && uvExist(uvindex_from, format)) {
 				array->SetUv(j, uvindex, array->GetUv(j, uvindex_from));
 			}
 
-			if (0 <= uvindex && uvindex < format.uvSize) {
-				const mt::vec2_packed& uv = array->GetUv(j, uvindex);
-				array->SetUv(j, uvindex, (transform * mt::vec3(uv.x, uv.y, 0.0f)).xy());
-			}
-			else if (uvindex == -1) {
+			// Transform all layers.
+			if (uvindex == -1) {
 				for (unsigned short k = 0; k < format.uvSize; ++k) {
 					const mt::vec2_packed& uv = array->GetUv(j, k);
 					array->SetUv(j, k, (transform * mt::vec3(uv.x, uv.y, 0.0f)).xy());
 				}
 			}
+			// Transform one layer.
+			else if (uvExist(uvindex, format)) {
+				const mt::vec2_packed& uv = array->GetUv(j, uvindex);
+				array->SetUv(j, uvindex, (transform * mt::vec3(uv.x, uv.y, 0.0f)).xy());
+			}
 		}
 
 		array->NotifyUpdate(RAS_DisplayArray::UVS_MODIFIED);