Fix 100% CPU usage with pane open (since 9e356a7e6)

And make Zotero.Item.prototype.fileExists() check the file regardless of
whether there's a cached state.

chrome/content/zotero/xpcom/data/item.js

@@ -2090,6 +2090,7 @@ Zotero.Item.prototype.getFilePathAsync = Zotero.Promise.coroutine(function* () {
 			return false;
 		}
 		
+		this._updateAttachmentStates(true);
 		return path;
 	}
 	
@@ -2215,10 +2216,6 @@ Zotero.Item.prototype.getFilename = function () {
  * This is updated only initially and on subsequent getFilePathAsync() calls.
  */
 Zotero.Item.prototype.fileExists = Zotero.Promise.coroutine(function* () {
-	if (this._fileExists !== null) {
-		return this._fileExists;
-	}
-	
 	if (!this.isAttachment()) {
 		throw new Error("Zotero.Item.fileExists() can only be called on attachment items");
 	}

test/tests/itemTest.js

@@ -616,6 +616,57 @@ describe("Zotero.Item", function () {
 		})
 	})
 	
+	
+	describe("#getBestAttachmentState()", function () {
+		it("should cache state for an existing file", function* () {
+			var parentItem = yield createDataObject('item');
+			var file = getTestDataDirectory();
+			file.append('test.png');
+			var childItem = yield Zotero.Attachments.importFromFile({
+				file,
+				parentItemID: parentItem.id
+			});
+			yield parentItem.getBestAttachmentState();
+			assert.equal(parentItem.getBestAttachmentStateCached(), 1);
+		})
+		
+		it("should cache state for a missing file", function* () {
+			var parentItem = yield createDataObject('item');
+			var file = getTestDataDirectory();
+			file.append('test.png');
+			var childItem = yield Zotero.Attachments.importFromFile({
+				file,
+				parentItemID: parentItem.id
+			});
+			let path = yield childItem.getFilePathAsync();
+			yield OS.File.remove(path);
+			yield parentItem.getBestAttachmentState();
+			assert.equal(parentItem.getBestAttachmentStateCached(), -1);
+		})
+	})
+	
+	
+	describe("#fileExists()", function () {
+		it("should cache state for an existing file", function* () {
+			var file = getTestDataDirectory();
+			file.append('test.png');
+			var item = yield Zotero.Attachments.importFromFile({ file });
+			yield item.fileExists();
+			assert.equal(item.fileExistsCached(), true);
+		})
+		
+		it("should cache state for a missing file", function* () {
+			var file = getTestDataDirectory();
+			file.append('test.png');
+			var item = yield Zotero.Attachments.importFromFile({ file });
+			let path = yield item.getFilePathAsync();
+			yield OS.File.remove(path);
+			yield item.fileExists();
+			assert.equal(item.fileExistsCached(), false);
+		})
+	})
+	
+	
 	describe("#setTags", function () {
 		it("should save an array of tags in API JSON format", function* () {
 			var tags = [