Don't crash in wxWebView under OS X if custom URI is invalid.

Don't assume that wxWebViewHandler::GetFile() always returns a valid pointer,
it may fail and return NULL, e.g. for a non-existent VFS location.

Closes #15254.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74239 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/webview_webkit.mm

@@ -1291,9 +1291,23 @@ wxString nsErrorToWxHtmlError(NSError* error, wxWebViewNavigationError* out)
     NSURLRequest *request = [self request];
 	NSString* path = [[request URL] absoluteString];
 
+    id<NSURLProtocolClient> client = [self client];
+
     wxString wxpath = wxStringWithNSString(path);
     wxString scheme = wxStringWithNSString([[request URL] scheme]);
     wxFSFile* file = g_stringHandlerMap[scheme]->GetFile(wxpath);
+
+    if (!file)
+    {
+        NSError *error = [[NSError alloc] initWithDomain:NSURLErrorDomain
+                            code:NSURLErrorFileDoesNotExist
+                            userInfo:nil];
+
+        [client URLProtocol:self didFailWithError:error];
+
+        return;
+    }
+
     size_t length = file->GetStream()->GetLength();
 
 
@@ -1307,8 +1321,6 @@ wxString nsErrorToWxHtmlError(NSError* error, wxWebViewNavigationError* out)
     file->GetStream()->Read(buffer, length);
     NSData *data = [[NSData alloc] initWithBytesNoCopy:buffer length:length];
 
-    id<NSURLProtocolClient> client = [self client];
-
     //We do not support caching anything yet
 	[client URLProtocol:self didReceiveResponse:response
             cacheStoragePolicy:NSURLCacheStorageNotAllowed];