Validate custom URL template string once, not once per line

Fixes #26

Test Plan:
Made `getTemplate` return null, then triggered blame. Before this change one
error would appear for every line. After this change, a single error appears.

Author: dmnd

lib/controllers/blameViewController.js

@@ -2,6 +2,7 @@ const $ = require('atom').$;
 const React = require('atom').React;
 const BlameListView = require('../views/blame-list-view');
 const RemoteRevision = require('../util/RemoteRevision');
+const errorController = require('./errorController');
 
 
 /**
@@ -15,12 +16,18 @@ const RemoteRevision = require('../util/RemoteRevision');
 function toggleBlame(projectBlamer) {
   var editorView = atom.workspaceView.getActiveView();
   var editor = editorView.getEditor();
+  var filePath = editor.getPath();
 
   if (!editorView.blameView) {
-    var filePath = atom.workspace.activePaneItem.getPath();
     var remoteUrl = projectBlamer.repo.getOriginUrl(filePath);
-    var remoteRevision = RemoteRevision.create(remoteUrl);
-    // TODO: validate the RemoteRevision here
+    var remoteRevision;
+    try {
+      remoteRevision = RemoteRevision.create(remoteUrl);
+    } catch (e) {
+      // the only exception possible occurs when the template string is invalid
+      errorController.showError('error-no-custom-url-specified');
+      return;
+    }
 
     // insert the BlameListView after the gutter div
     var mountPoint = $('<div>', {'class': 'git-blame-mount'});
@@ -29,7 +36,7 @@ function toggleBlame(projectBlamer) {
     editorView.blameView = React.renderComponent(new BlameListView({
       projectBlamer: projectBlamer,
       remoteRevision: remoteRevision,
-      filePath: editor.getPath(),
+      filePath: filePath,
       lineCount: editor.getLineCount(),
       scrollbar: editorView.find('.vertical-scrollbar')
     }), mountPoint[0]);

lib/util/RemoteRevision.js

@@ -13,8 +13,12 @@ function RemoteRevision(remote) {
 // ================
 
 RemoteRevision.create = function(remoteUrl) {
-  return new RemoteRevision(remoteUrl);
-}
+  var rr = new RemoteRevision(remoteUrl);
+  if (!rr.getTemplate()) {
+    throw "Cannot create RemoteRevision with invalid template";
+  }
+  return rr;
+};
 
 // ================
 // Instance Methods
@@ -35,10 +39,9 @@ _.extend(RemoteRevision.prototype, {
 
   url: function(revision) {
     var template = this.getTemplate();
-
     if (!template) {
-      errorController.showError('error-no-custom-url-specified');
-      return;
+      // this should be impossible, so throw
+      throw "No template present in RemoteRevision";
     }
 
     // create data object used to render template string
@@ -47,6 +50,7 @@ _.extend(RemoteRevision.prototype, {
 
     // ensure we have all the correct vars in the template data
     if (!this.verifyTemplateData(data)) {
+      // TODO: validate this upon creation
       errorController.showError('error-problem-parsing-data-from-remote');
       return;
     }