Fixes autosave submit handler

Clear autosave timeout in submit handler to prevent reinserting data to
local storage after the submit. Also, prevent attaching the same submit
handler in every autosave call.

src/js/simplemde.js

@@ -1601,10 +1601,22 @@ SimpleMDE.prototype.autosave = function() {
 			return;
 		}
 
-		if(simplemde.element.form != null && simplemde.element.form != undefined) {
-			simplemde.element.form.addEventListener("submit", function() {
-				localStorage.removeItem("smde_" + simplemde.options.autosave.uniqueId);
-			});
+		if(this.options.autosave.binded !== true) {
+			if(simplemde.element.form != null && simplemde.element.form != undefined) {
+				simplemde.element.form.addEventListener("submit", function() {
+					clearTimeout(simplemde.autosaveTimeoutId);
+					simplemde.autosaveTimeoutId = undefined;
+
+					localStorage.removeItem("smde_" + simplemde.options.autosave.uniqueId);
+
+					// Restart autosaving in case the submit will be cancelled down the line
+					setTimeout(function() {
+						simplemde.autosave();
+					}, 10000);
+				});
+			}
+
+			this.options.autosave.binded = true;
 		}
 
 		if(this.options.autosave.loaded !== true) {