[NM-279] Empty pages aren't shown in nimble (#111)

* [NM-279] Empty pages aren't shown in nimble

* rename PageDocument method 'onPageLoad' to 'onPageDidLoad'

Plugins/InterfaceBuilder/InterfaceBuilder/Sources/PageDocument.swift

@@ -45,6 +45,7 @@ public final class PageDocument: NimbleDocument, SVGDocumentProtocol {
 
   public override func read(from url: URL, ofType typeName: String) throws {
     adapter.load(url.path)
+    onPageDidLoad()
   }
 
   public override func data(ofType typeName: String) throws -> Data {
@@ -55,6 +56,15 @@ public final class PageDocument: NimbleDocument, SVGDocumentProtocol {
     }
     return "".data(using: .utf8)!
   }
+
+  private func onPageDidLoad() {
+    if let size = adapter.page?.size {
+      if size.width == 0 || size.height == 0 {
+        size.width = 320
+        size.height = 480
+      }
+    }
+  }
 }
 
 extension PageDocument: Document {
@@ -78,11 +88,7 @@ extension PageDocument: CreatableDocument {
   public static func createUntitledDocument() -> Document? {
     let doc = PageDocument()
     doc.adapter.loadTemplatePage()
-
-    if let size = doc.adapter.page?.size {
-      size.width = 320
-      size.height = 480
-    }
+    doc.onPageDidLoad()
 
     return doc
   }