Don't issue draw call if there is nothing to draw.

src/IndexedMesh.cpp

@@ -33,6 +33,8 @@ IndexedMesh* IndexedMesh::setIndexBuffer(Buffer* buffer) {
 }
 
 void IndexedMesh::draw() {
+    if(!_indexCount) return;
+
     bind();
 
     /** @todo Start at given index */

src/Mesh.cpp

@@ -90,6 +90,8 @@ Mesh* Mesh::setVertexCount(GLsizei vertexCount) {
 }
 
 void Mesh::draw() {
+    if(!_vertexCount) return;
+
     bind();
 
     /** @todo Start at given index */