Don't clear item type set in constructor when loading primary data

Generally, don't clear the change state for primaryData when calling
loadPrimaryData() on an item that doesn't exist. Specifically, this
fixes an issue where calling loadPrimaryData() on a nonexistent item
after setting a libraryID and key would also clear any item type set in
the constructor. The same would apply for props set in the
Collection/Search constructors.

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

@@ -639,7 +639,6 @@ Zotero.DataObject.prototype.loadPrimaryData = Zotero.Promise.coroutine(function*
 			throw new Error(this._ObjectType + " " + (id ? id : libraryID + "/" + key)
 				+ " not found in Zotero." + this._ObjectType + ".loadPrimaryData()");
 		}
-		this._clearChanged('primaryData');
 		
 		// If object doesn't exist, mark all data types as loaded
 		this._markAllDataTypeLoadStates(true);

test/tests/dataObjectTest.js

@@ -210,7 +210,16 @@ describe("Zotero.DataObject", function() {
 				yield obj.loadPrimaryData();
 				assert.equal(obj.version, objs[type].version);
 			}
-		})
+		});
+		
+		it("shouldn't overwrite item type set in constructor", async function () {
+			var item = new Zotero.Item('book');
+			item.libraryID = Zotero.Libraries.userLibraryID;
+			item.key = Zotero.DataObjectUtilities.generateKey();
+			await item.loadPrimaryData();
+			var saved = await item.saveTx();
+			assert.ok(saved);
+		});
 	})
 	
 	describe("#loadAllData()", function () {