patch 8.0.1556: may not parse the t_RS response correctly

Problem:    May not parse the t_RS response correctly, resulting in wrong
            characters in the input stream.
Solution:   When the t_RS response is partly received wait for more
            characters.

src/term.c

@@ -4866,7 +4866,7 @@ check_termcode(
 	     * {tail} can be Esc>\ or STERM
 	     *
 	     * Check for cursor shape response from xterm:
-	     * {lead}1$r<number> q{tail}
+	     * {lead}1$r<digit> q{tail}
 	     *
 	     * {lead} can be <Esc>P or DCS
 	     * {tail} can be Esc>\ or STERM
@@ -4897,14 +4897,23 @@ check_termcode(
 			break;
 		    }
 		  }
-		else if ((len >= j + 6 && isdigit(argp[3]))
-			&& argp[4] == ' '
-			&& argp[5] == 'q')
+		else
 		{
-		    /* cursor shape response */
-		    i = j + 6;
-		    if ((tp[i] == ESC && i + 1 < len && tp[i + 1] == '\\')
-			    || tp[i] == STERM)
+		    /* Probably the cursor shape response.  Make sure that "i"
+		     * is equal to "len" when there are not sufficient
+		     * characters. */
+		    for (i = j + 3; i < len; ++i)
+		    {
+			if (i - j == 3 && !isdigit(tp[i]))
+			    break;
+			if (i - j == 4 && tp[i] != ' ')
+			    break;
+			if (i - j == 5 && tp[i] != 'q')
+			    break;
+			if (i - j == 6 && tp[i] != ESC && tp[i] != STERM)
+			    break;
+			if ((i - j == 6 && tp[i] == STERM)
+			 || (i - j == 7 && tp[i] == '\\'))
 			{
 			    int number = argp[3] - '0';
 
@@ -4922,10 +4931,12 @@ check_termcode(
 
 			    key_name[0] = (int)KS_EXTRA;
 			    key_name[1] = (int)KE_IGNORE;
-			slen = i + 1 + (tp[i] == ESC);
+			    slen = i + 1;
 # ifdef FEAT_EVAL
 			    set_vim_var_string(VV_TERMSTYLERESP, tp, slen);
 # endif
+			    break;
+			}
 		    }
 		}
 

src/version.c

@@ -778,6 +778,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1556,
 /**/
     1555,
 /**/