patch 8.1.0426: accessing invalid memory in SmcOpenConnection()

Problem:    Accessing invalid memory in SmcOpenConnection().
Solution:   Reduce size of errorstring by one. (Dominique Pelle, closes #3469)

src/os_unix.c

@@ -8032,7 +8032,7 @@ xsmp_init(void)
 	    &smcallbacks,
 	    NULL,
 	    &xsmp.clientid,
-	    sizeof(errorstring),
+	    sizeof(errorstring) - 1,
 	    errorstring);
     if (xsmp.smcconn == NULL)
     {

src/testdir/test_startup.vim

@@ -272,7 +272,7 @@ endfunc
 " Test the -V[N]{filename} argument to set the 'verbose' option to N
 " and set 'verbosefile' to filename.
 func Test_V_file_arg()
-  if RunVim([], [], ' --clean -X -V2Xverbosefile -c "set verbose? verbosefile?" -cq')
+  if RunVim([], [], ' --clean -V2Xverbosefile -c "set verbose? verbosefile?" -cq')
     let out = join(readfile('Xverbosefile'), "\n")
     call assert_match("sourcing \"$VIMRUNTIME[\\/]defaults\.vim\"\n", out)
     call assert_match("\n  verbose=2\n", out)

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    426,
 /**/
     425,
 /**/