Fix T47353: Project paint ignores small faces

When zoomed out - faces < 0.5 pixels across a diagonal aren't so rare,
so culling them can ignore small faces.

source/blender/editors/sculpt_paint/paint_image_proj.c

@@ -2096,8 +2096,9 @@ static void project_bucket_clip_face(
 
 	/* detect pathological case where face the three vertices are almost collinear in screen space.
 	 * mostly those will be culled but when flood filling or with smooth shading it's a possibility */
-	if (dist_squared_to_line_v2(v1coSS, v2coSS, v3coSS) < 0.5f ||
-	    dist_squared_to_line_v2(v2coSS, v3coSS, v1coSS) < 0.5f)
+	if (min_fff(dist_squared_to_line_v2(v1coSS, v2coSS, v3coSS),
+	            dist_squared_to_line_v2(v2coSS, v3coSS, v1coSS),
+	            dist_squared_to_line_v2(v3coSS, v1coSS, v2coSS)) < PROJ_PIXEL_TOLERANCE)
 	{
 		collinear = true;
 	}