Fixed is_playing funtion (was reporting wrong), closes #13928

Made error reporting to opcode_set in gdscript a bit clearer

modules/gdscript/gdscript_function.cpp

@@ -515,7 +515,7 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 					} else {
 						v = "of type '" + _get_var_type(index) + "'";
 					}
-					err_text = "Invalid set index " + v + " (on base: '" + _get_var_type(dst) + "').";
+					err_text = "Invalid set index " + v + " (on base: '" + _get_var_type(dst) + "') with value of type '"+_get_var_type(value)+"'";
 					OPCODE_BREAK;
 				}
 #endif
@@ -574,7 +574,7 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 #ifdef DEBUG_ENABLED
 				if (!valid) {
 					String err_type;
-					err_text = "Invalid set index '" + String(*index) + "' (on base: '" + _get_var_type(dst) + "').";
+					err_text = "Invalid set index '" + String(*index) + "' (on base: '" + _get_var_type(dst) + "') with value of type '"+_get_var_type(value)+"'.";
 					OPCODE_BREAK;
 				}
 #endif

scene/2d/animated_sprite.cpp

@@ -568,7 +568,7 @@ void AnimatedSprite::stop() {
 
 bool AnimatedSprite::is_playing() const {
 
-	return is_processing();
+	return playing;
 }
 
 void AnimatedSprite::_reset_timeout() {