Fix T80782 GPU: Curve editing widget point size broken after recent commit

This was caused by a faulty default where program point size was used.

source/blender/gpu/intern/gpu_state.cc

@@ -351,7 +351,7 @@ StateManager::StateManager(void)
 
   mutable_state.depth_range[0] = 0.0f;
   mutable_state.depth_range[1] = 1.0f;
-  mutable_state.point_size = 1.0f;
+  mutable_state.point_size = -1.0f; /* Negative is not using point size. */
   mutable_state.line_width = 1.0f;
   mutable_state.stencil_write_mask = 0x00;
   mutable_state.stencil_compare_mask = 0x00;

source/blender/gpu/intern/gpu_state_private.hh

@@ -98,7 +98,7 @@ union GPUStateMutable {
     /* Viewport State */
     /** TODO remove */
     float depth_range[2];
-    /** Negative if using program point size. */
+    /** Positive if using program point size. */
     /* TODO(fclem) should be passed as uniform to all shaders. */
     float point_size;
     /** Not supported on every platform. Prefer using wideline shader. */