GPU: Avoid invalid GL API usage

Drawing with 0 sized buffer is prohibited.

source/blender/gpu/opengl/gl_batch.cc

@@ -325,6 +325,8 @@ void GLBatch::draw(int v_first, int v_count, int i_first, int i_count)
 {
   this->bind(i_first);
 
+  BLI_assert(v_count > 0 && i_count > 0);
+
   GLenum gl_type = convert_prim_type_to_gl(prim_type);
 
   if (elem) {

source/blender/gpu/opengl/gl_drawlist.cc

@@ -151,6 +151,11 @@ void GLDrawList::append(GPUBatch *batch, int i_first, int i_count)
     v_count_ = batch->elem ? batch->elem->index_len : batch->verts[0]->vertex_len;
   }
 
+  if (v_count_ == 0) {
+    /* Nothing to draw. */
+    return;
+  }
+
   if (MDI_INDEXED) {
     GLDrawCommandIndexed *cmd = reinterpret_cast<GLDrawCommandIndexed *>(data_ + command_offset_);
     cmd->v_first = v_first_;