patch 8.2.1979: "term_opencmd" option of term_start() is truncated

Problem:    "term_opencmd" option of term_start() is truncated. (Sergey
            Vlasov)
Solution:   Allocate the buffer to hold the command. (closes #7284)
diff --git a/src/terminal.c b/src/terminal.c
index 0fb9f48..4e2ff14 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -3450,15 +3450,19 @@
 	if (term->tl_finish == TL_FINISH_OPEN
 				   && term->tl_buffer->b_nwindows == 0)
 	{
-	    char buf[50];
+	    char    *cmd = term->tl_opencmd == NULL
+				? "botright sbuf %d"
+				: (char *)term->tl_opencmd;
+	    size_t  len = strlen(cmd) + 50;
+	    char    *buf = alloc(len);
 
-	    // TODO: use term_opencmd
-	    ch_log(NULL, "terminal job finished, opening window");
-	    vim_snprintf(buf, sizeof(buf),
-		    term->tl_opencmd == NULL
-			    ? "botright sbuf %d"
-			    : (char *)term->tl_opencmd, fnum);
-	    do_cmdline_cmd((char_u *)buf);
+	    if (buf != NULL)
+	    {
+		ch_log(NULL, "terminal job finished, opening window");
+		vim_snprintf(buf, len, cmd, fnum);
+		do_cmdline_cmd((char_u *)buf);
+		vim_free(buf);
+	    }
 	}
 	else
 	    ch_log(NULL, "terminal job finished");
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index ece8120..16ad720 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -567,10 +567,12 @@
   call assert_fails("call term_start(cmd, {'term_opencmd': 'split %d and %s'})", 'E475:')
   call assert_fails("call term_start(cmd, {'term_opencmd': 'split % and %d'})", 'E475:')
 
-  call term_start(cmd, {'term_finish': 'open', 'term_opencmd': '4split | buffer %d'})
+  call term_start(cmd, {'term_finish': 'open', 'term_opencmd': '4split | buffer %d | let g:result = "opened the buffer in a window"'})
   close!
   call WaitForAssert({-> assert_equal(2, winnr('$'))}, waittime)
   call assert_equal(4, winheight(0))
+  call assert_equal('opened the buffer in a window', g:result)
+  unlet g:result
   bwipe
 endfunc
 
diff --git a/src/version.c b/src/version.c
index caf4db8..bb33bcb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1979,
+/**/
     1978,
 /**/
     1977,