Fix T103037: Regression: Grease Pencil Line Texture last point gets distorted

This was due to a missing endpoint case that wasn't handled in the port.

The last point still have to be discarded manually because of the
dot/stroke setting of the material.

The first test `ma1.x == -1` is not necessary anymore since the index
buffer do not contain this point (which was rendered using instance
rendering before.

Reviewed By: jbakker
Differential Revision: https://developer.blender.org/D16812

source/blender/draw/intern/shaders/common_gpencil_lib.glsl

@@ -187,6 +187,13 @@ vec4 gpencil_vertex(vec4 viewport_size,
       is_squares = false;
     }
 
+    /* Endpoints, we discard the vertices. */
+    if (!is_dot && ma2.x == -1) {
+      /* We set the vertex at the camera origin to generate 0 fragments. */
+      out_ndc = vec4(0.0, 0.0, -3e36, 0.0);
+      return out_ndc;
+    }
+
     /* Avoid using a vertex attribute for quad positioning. */
     float x = float(gl_VertexID & 1) * 2.0 - 1.0; /* [-1..1] */
     float y = float(gl_VertexID & 2) - 1.0;       /* [-1..1] */