patch 8.1.0279: 'incsearch' highlighting does not skip white space

Problem:    'incsearch' highlighting does not skip white space.
Solution:   Skip white space after the command. (issue #3321)

src/ex_getln.c

@@ -293,11 +293,12 @@ do_incsearch_highlighting(int firstc, incsearch_state_T *is_state,
 		// Skip over "substitute" to find the pattern separator.
 		for (p = cmd; ASCII_ISALPHA(*p); ++p)
 		    ;
-		if (*p != NUL
+		if (*skipwhite(p) != NUL
 			&& (STRNCMP(cmd, "substitute", p - cmd) == 0
 			    || STRNCMP(cmd, "global", p - cmd) == 0
 			    || STRNCMP(cmd, "vglobal", p - cmd) == 0))
 		{
+		    p = skipwhite(p);
 		    delim = *p++;
 		    end = skip_regexp(p, delim, p_magic, NULL);
 		    if (end > p || *end == delim)

src/testdir/dumps/Test_incsearch_substitute_05.dump

@@ -0,0 +1,9 @@
+|f+0&#ffffff0|o@1| |1| @64
+|f+1&&|o|o+0&&| |2| @64
+|f+0&#ffff4012|o|o+0&#ffffff0| |3| @64
+|f|o@1| |4| @64
+|f|o@1| |5| @64
+|f|o@1| |6| @64
+|f|o@1| |7| @64
+|f|o@1| |8| @64
+|:|2|,|3|s|u|b| @1|/|f|o> @57

src/testdir/test_search.vim

@@ -868,8 +868,14 @@ func Test_incsearch_substitute_dump()
   call term_sendkeys(buf, ':5,2s/foo')
   sleep 100m
   call VerifyScreenDump(buf, 'Test_incsearch_substitute_04', {})
-
   call term_sendkeys(buf, "\<Esc>")
+
+  " White space after the command is skipped
+  call term_sendkeys(buf, ':2,3sub  /fo')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_substitute_05', {})
+  call term_sendkeys(buf, "\<Esc>")
+
   call StopVimInTerminal(buf)
   call delete('Xis_subst_script')
 endfunc

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    279,
 /**/
     278,
 /**/