check for nullptr when freeing simple mesh

src/entity.cpp

@@ -51,7 +51,8 @@ entFree(entity& e)
 	roFree(e.render_objs);
 	e.render_objs = nullptr;
 	meFreeMeshGroup(e.meshes);
-	meFreeSimpleMesh(e.mesh);
+
+	if (e.mesh != nullptr) meFreeSimpleMesh(e.mesh);
 	e.mesh = nullptr;
 }
 

src/mesh.cpp

@@ -94,6 +94,7 @@ meFreeMeshGroup(mesh_group& mesh_group)
 void
 meFreeSimpleMesh(simple_mesh* mesh)
 {
+	assert(mesh != nullptr);
 	utilSafeFree(mesh->vertices);
 	mesh->vertices = nullptr;
 	utilSafeFree(mesh->vert_colors);

src/renderer.cpp

@@ -1,7 +1,4 @@
 
-#include <vector>
-#include <cmath> // trig functions
-
 #if defined (_WIN32)
 	#include <SDL.h>
 #else