QPlainTextEdit crashes when using IME on Android

Hi there.

This issue happens if the cursor reaches the the bottom of the QPlainTextEdit. If the current line have N spaces left(see testcase1_1.jpg and testcase2_1.jpg), and I input N+1 or more characters in the IME(see testcase1_2.jpg and testcase2_2.jpg), the application will crash when I confirm the input.

This issue doesn't happen if I paste a piece of text with N+1 characters in it.

The traceback file shows that something might be wrong in QTextLine::naturalTextRect()

I've tested it on two different IMEs and got the same result.

Steps to reproduce:

1. build an application on Android with a QPlainTextEdit in it, then run it.
2. Keep typing something in the QPlainTextEdit until the cursor reaches the bottom.
3. Type something and keep N spaces in the current line.
4. Type N+1 characters in the IME
5. confirm the input in the IME, then the application crashes.

I've created a minimal project with .pro.user file in it to reproduce this issue(see qtbug.zip). I hope it helps.