Clamp the modulated border colors to valid values.

Author: nical

webrender/res/ps_border_corner.glsl

@@ -110,10 +110,10 @@ void write_color(vec4 color0, vec4 color1, int style, vec2 delta, int instance_k
             break;
     }
 
-    vColor00 = vec4(color0.rgb * modulate.x, color0.a);
-    vColor01 = vec4(color0.rgb * modulate.y, color0.a);
-    vColor10 = vec4(color1.rgb * modulate.z, color1.a);
-    vColor11 = vec4(color1.rgb * modulate.w, color1.a);
+    vColor00 = vec4(clamp(color0.rgb * modulate.x, vec3(0.0), vec3(1.0)), color0.a);
+    vColor01 = vec4(clamp(color0.rgb * modulate.y, vec3(0.0), vec3(1.0)), color0.a);
+    vColor10 = vec4(clamp(color1.rgb * modulate.z, vec3(0.0), vec3(1.0)), color1.a);
+    vColor11 = vec4(clamp(color1.rgb * modulate.w, vec3(0.0), vec3(1.0)), color1.a);
 }
 
 int select_style(int color_select, vec2 fstyle) {