patch 8.2.0259: terminal in popup test sometimes fails

Problem:    Terminal in popup test sometimes fails.
Solution:   Clear the command line.

Author: brammool

src/testdir/dumps/Test_terminal_popup_1.dump

@@ -8,7 +8,7 @@
 |7| @12|║+0#0000001#ffd7ff255|~+0#4040ff13#ffffff0| @43|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@13
 |8| @12|║+0#0000001#ffd7ff255|~+0#4040ff13#ffffff0| @43|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@13
 |9| @12|║+0#0000001#ffd7ff255|~+0#4040ff13#ffffff0| @43|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@13
-|1|0| @11|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@26|1|,|1| @10|A|l@1| |║+0#0000001#ffd7ff255| +0#0000000#ffffff0@13
+|1|0| @11|║+0#0000001#ffd7ff255|:+0#0000000#ffffff0| @25|1|,|1| @10|A|l@1| |║+0#0000001#ffd7ff255| +0#0000000#ffffff0@13
 |1@1| @11|╚+0#0000001#ffd7ff255|═@44|⇲| +0#0000000#ffffff0@13
 |1|2| @72
 |1|3| @72

src/testdir/test_terminal.vim

@@ -2353,6 +2353,7 @@ func Test_terminal_in_popup()
 	\ ]
   call writefile(lines, 'XtermPopup')
   let buf = RunVimInTerminal('-S XtermPopup', #{rows: 15})
+  call term_sendkeys(buf, ":\<CR>")
   call VerifyScreenDump(buf, 'Test_terminal_popup_1', {})
 
   call term_sendkeys(buf, ":q\<CR>")

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    259,
 /**/
     258,
 /**/