[models] Fix M3D vertex color import. (#2878)

* Fix vertex color import for .m3d

* Only load vertex colors when color map and/or materials are present

* Only execute when color array is present

---------

Co-authored-by: Uneven Prankster <unevenprankster@pm.me>

src/rmodels.c

@@ -5633,11 +5633,9 @@ static Model LoadM3D(const char *fileName)
                 model.meshes[k].texcoords = (float *)RL_CALLOC(model.meshes[k].vertexCount*2, sizeof(float));
                 model.meshes[k].normals = (float *)RL_CALLOC(model.meshes[k].vertexCount*3, sizeof(float));
                 
-                // without material, we rely on vertex colors
-                if (mi == M3D_UNDEF && model.meshes[k].colors == NULL)
+                if(m3d->cmap != NULL || mi != M3D_UNDEF)
                 {
                     model.meshes[k].colors = RL_CALLOC(model.meshes[k].vertexCount*4, sizeof(unsigned char));
-                    for (j = 0; j < model.meshes[k].vertexCount*4; j += 4) memcpy(&model.meshes[k].colors[j], &WHITE, 4);
                 }
                 
                 if (m3d->numbone && m3d->numskin)
@@ -5662,10 +5660,10 @@ static Model LoadM3D(const char *fileName)
             model.meshes[k].vertices[l * 9 + 6] = m3d->vertex[m3d->face[i].vertex[2]].x*m3d->scale;
             model.meshes[k].vertices[l * 9 + 7] = m3d->vertex[m3d->face[i].vertex[2]].y*m3d->scale;
             model.meshes[k].vertices[l * 9 + 8] = m3d->vertex[m3d->face[i].vertex[2]].z*m3d->scale;
-
-            if (mi == M3D_UNDEF)
+            
+            // without vertex color (full transparency), we use the default color
+            if(model.meshes[k].colors != NULL)
             {
-                // without vertex color (full transparency), we use the default color
                 if (m3d->vertex[m3d->face[i].vertex[0]].color & 0xFF000000)
                     memcpy(&model.meshes[k].colors[l * 12 + 0], &m3d->vertex[m3d->face[i].vertex[0]].color, 4);
                 if (m3d->vertex[m3d->face[i].vertex[1]].color & 0xFF000000)