Cordova: Close sheet modal when back button pressed

www/assets/js/platform.js

@@ -113,7 +113,12 @@ function initCordova() {
     platform_type = "cordova";
     // Handle back button to close things
     document.addEventListener("backbutton", function (event) {
+        // Close map sheet if it's open
+        if ($(".sheet-modal").hasClass("modal-in")) {
+            app.sheet.close();
+        } else {
             router.back({force: true, ignoreCache: true});
+        }
     }, false);
     document.addEventListener("deviceready", function () {
         if (localStorage.getItem("wakelock") == "true") {