patch 9.1.0601: Wrong cursor position with 'breakindent' when wide char doesn't fit

Problem:  Wrong cursor position with 'breakindent' when a double-width
          character doesn't fit in a screen line (mikoto2000)
Solution: Include the width of the 'breakindent' properly.
          (zeertzjq)

fixes: #15289
closes: #15290

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_textprop.vim b/src/testdir/test_textprop.vim
index 2bf2834..57277f7 100644
--- a/src/testdir/test_textprop.vim
+++ b/src/testdir/test_textprop.vim
@@ -2901,6 +2901,10 @@
   call writefile(lines, 'XscriptPropsBeforeDoubleWidthWrap', 'D')
   let buf = RunVimInTerminal('-S XscriptPropsBeforeDoubleWidthWrap', #{rows: 3, cols: 50})
   call VerifyScreenDump(buf, 'Test_prop_inserts_text_before_double_width_wrap_1', {})
+  call term_sendkeys(buf, 'g0')
+  call VerifyScreenDump(buf, 'Test_prop_inserts_text_before_double_width_wrap_2', {})
+  call term_sendkeys(buf, ":set showbreak=+++\<CR>")
+  call VerifyScreenDump(buf, 'Test_prop_inserts_text_before_double_width_wrap_3', {})
 
   call StopVimInTerminal(buf)
 endfunc