truncate redbox error

Summary: If a redbox error is too long it's not shown at all:
{F24443416}
This diff truncates it to its first 10000 chars, which should be good enough:
{F24443417}

The reason is a limitation of UILabel which backs text property on the used UITableViewCell.
Ideally we would use a custom cell with UITextView, but I don't feel there is any value in displaying super long error messages in a redbox.

public

Reviewed By: jspahrsummers, nicklockwood

Differential Revision: D2690638

fb-gh-sync-id: d9b3fcecd2602e8c2618afe1bb97221c2e506605

React/Modules/RCTRedBox.m

@@ -107,7 +107,8 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
 {
   if ((self.hidden && shouldShow) || (!self.hidden && [_lastErrorMessage isEqualToString:message])) {
     _lastStackTrace = stack;
-    _lastErrorMessage = message;
+    // message is displayed using UILabel, which is unable to render text of unlimited length, so we truncate it
+    _lastErrorMessage = [message substringToIndex:MIN(10000, message.length)];
 
     [_stackTraceTableView reloadData];