fix(ios): resolve crash on event dispatch

Author: alpha0010

ios/PdfView.mm

@@ -35,14 +35,14 @@ - (instancetype)initWithFrame:(CGRect)frame
         __weak PdfView *weakSelf = self;
         _view.onPdfError = ^(NSString *message) {
             PdfView *strongSelf = weakSelf;
-            if (strongSelf) {
+            if (strongSelf && strongSelf->_eventEmitter) {
                 static_cast<const PdfViewEventEmitter &>(*strongSelf->_eventEmitter)
                     .onPdfError({[message UTF8String]});
             }
         };
         _view.onPdfLoadComplete = ^(NSInteger width, NSInteger height) {
             PdfView *strongSelf = weakSelf;
-            if (strongSelf) {
+            if (strongSelf && strongSelf->_eventEmitter) {
                 PdfViewEventEmitter::OnPdfLoadComplete evt;
                 evt.width = static_cast<int>(width);
                 evt.height = static_cast<int>(height);

ios/PdfView.swift

@@ -290,10 +290,13 @@ public class PdfView: UIView {
     }
 
     private func dispatchOnError(message: String) {
-        guard let dispatcher = onPdfError else {
-            return
+        // Queue message to give RN core a chance to init event emitters.
+        DispatchQueue.main.async {
+            guard let dispatcher = self.onPdfError else {
+                return
+            }
+            dispatcher(message)
         }
-        dispatcher(message)
     }
 
     private func dispatchOnLoadComplete(pageWidth: CGFloat, pageHeight: CGFloat) {