patch 8.2.5058: input() does not handle composing characters properly

Problem:    input() does not handle composing characters properly.
Solution:   Use mb_cptr2char_adv() instead of mb_ptr2char_adv().
            (closes #10527)
diff --git a/src/getchar.c b/src/getchar.c
index 55fad1c..03d90ac 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -669,7 +669,7 @@
 	}
 	else
 	{
-	    c = mb_ptr2char_adv(&s);
+	    c = mb_cptr2char_adv(&s);
 	    if (c == CAR || c == NL || c == ESC)
 		c = ' ';
 	    stuffcharReadbuff(c);
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index af07a64..f55e846 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -1545,6 +1545,10 @@
   call feedkeys(":let c = input('name? ', \"x\\<BS>y\")\<CR>\<CR>", 'xt')
   call assert_equal('y', c)
 
+  " Test for using text with composing characters as default input
+  call feedkeys(":let c = input('name? ', \"ã̳\")\<CR>\<CR>", 'xt')
+  call assert_equal('ã̳', c)
+
   " Test for using <CR> as default input
   call feedkeys(":let c = input('name? ', \"\\<CR>\")\<CR>x\<CR>", 'xt')
   call assert_equal(' x', c)
diff --git a/src/version.c b/src/version.c
index 254b5f1..744fad6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -735,6 +735,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    5058,
+/**/
     5057,
 /**/
     5056,