Overlay-Next: Fix glitches with the grid

The vertex array was allocating uninitialized memory.
This fixes the API usage mistake and do the
intended reserve call.

source/blender/draw/engines/overlay/overlay_next_shape.cc

@@ -1376,7 +1376,8 @@ ShapeCache::ShapeCache()
       steps[i] = -1.0f + float(i * 2) / resolution;
     }
 
-    Vector<Vertex> verts(resolution * resolution * 6);
+    Vector<Vertex> verts;
+    verts.reserve(resolution * resolution * 6);
     for (const int x : IndexRange(resolution)) {
       for (const int y : IndexRange(resolution)) {
         verts.append(Vertex{{steps[x], steps[y], 0.0f}});