Don't use prepass threshold with alpha scissor

drivers/gles2/shaders/scene.glsl

@@ -1695,9 +1695,13 @@ FRAGMENT_SHADER_CODE
 #endif // ALPHA_SCISSOR_USED
 
 #ifdef USE_DEPTH_PREPASS
+#if !defined(ALPHA_SCISSOR_USED)
+
 	if (alpha < 0.1) {
 		discard;
 	}
+
+#endif // not ALPHA_SCISSOR_USED
 #endif // USE_DEPTH_PREPASS
 
 #endif // !USE_SHADOW_TO_OPACITY
@@ -2255,9 +2259,13 @@ FRAGMENT_SHADER_CODE
 #endif // ALPHA_SCISSOR_USED
 
 #ifdef USE_DEPTH_PREPASS
+#if !defined(ALPHA_SCISSOR_USED)
+
 	if (alpha < 0.1) {
 		discard;
 	}
+
+#endif // not ALPHA_SCISSOR_USED
 #endif // USE_DEPTH_PREPASS
 
 #endif // !USE_SHADOW_TO_OPACITY

drivers/gles3/shaders/scene.glsl

@@ -1902,11 +1902,13 @@ FRAGMENT_SHADER_CODE
 #endif // ALPHA_SCISSOR_USED
 
 #ifdef USE_OPAQUE_PREPASS //ubershader-runtime
+#if !defined(ALPHA_SCISSOR_USED)
 
 	if (alpha < opaque_prepass_threshold) {
 		discard;
 	}
 
+#endif // not ALPHA_SCISSOR_USED
 #endif // USE_OPAQUE_PREPASS //ubershader-runtime
 
 #endif // !USE_SHADOW_TO_OPACITY
@@ -2282,10 +2284,13 @@ FRAGMENT_SHADER_CODE
 #endif // ALPHA_SCISSOR_USED
 
 #ifdef USE_OPAQUE_PREPASS //ubershader-runtime
+#if !defined(ALPHA_SCISSOR_USED)
+
 	if (alpha < opaque_prepass_threshold) {
 		discard;
 	}
 
+#endif // not ALPHA_SCISSOR_USED
 #endif // USE_OPAQUE_PREPASS //ubershader-runtime
 
 #endif // USE_SHADOW_TO_OPACITY