patch 8.2.3393: escaping for fish shell is skipping some characters

Problem:    Escaping for fish shell is skipping some characters.
Solution:   Escape character after backslash if needed. (Jason Cox,
            closes #8827)
diff --git a/src/strings.c b/src/strings.c
index 0c9e20d..d2d37d8 100644
--- a/src/strings.c
+++ b/src/strings.c
@@ -281,6 +281,7 @@
 	    {
 		*d++ = '\\';
 		*d++ = *p++;
+		continue;
 	    }
 
 	    MB_COPY_CHAR(p, d);
diff --git a/src/testdir/test_shell.vim b/src/testdir/test_shell.vim
index fa11f08..a6aa10e 100644
--- a/src/testdir/test_shell.vim
+++ b/src/testdir/test_shell.vim
@@ -61,21 +61,21 @@
   for e in shells
     exe 'set shell=' .. e[0]
     if e[0] =~# '.*csh$' || e[0] =~# '.*csh.exe$'
-      let str1 = "'cmd \"arg1\" '\\''arg2'\\'' \\!%# \\'"
-      let str2 = "'cmd \"arg1\" '\\''arg2'\\'' \\\\!\\%\\# \\'"
+      let str1 = "'cmd \"arg1\" '\\''arg2'\\'' \\!%# \\'\\'' \\\\! \\% \\#'"
+      let str2 = "'cmd \"arg1\" '\\''arg2'\\'' \\\\!\\%\\# \\'\\'' \\\\\\! \\\\% \\\\#'"
     elseif e[0] =~# '.*powershell$' || e[0] =~# '.*powershell.exe$'
           \ || e[0] =~# '.*pwsh$' || e[0] =~# '.*pwsh.exe$'
-      let str1 = "'cmd \"arg1\" ''arg2'' !%# \\'"
-      let str2 = "'cmd \"arg1\" ''arg2'' \\!\\%\\# \\'"
+      let str1 = "'cmd \"arg1\" ''arg2'' !%# \\'' \\! \\% \\#'"
+      let str2 = "'cmd \"arg1\" ''arg2'' \\!\\%\\# \\'' \\\\! \\\\% \\\\#'"
     elseif e[0] =~# '.*fish$' || e[0] =~# '.*fish.exe$'
-      let str1 = "'cmd \"arg1\" '\\''arg2'\\'' !%# \\\\'"
-      let str2 = "'cmd \"arg1\" '\\''arg2'\\'' \\!\\%\\# \\\\'"
+      let str1 = "'cmd \"arg1\" '\\''arg2'\\'' !%# \\\\'\\'' \\\\! \\\\% \\\\#'"
+      let str2 = "'cmd \"arg1\" '\\''arg2'\\'' \\!\\%\\# \\\\'\\'' \\\\\\! \\\\\\% \\\\\\#'"
     else
-      let str1 = "'cmd \"arg1\" '\\''arg2'\\'' !%# \\'"
-      let str2 = "'cmd \"arg1\" '\\''arg2'\\'' \\!\\%\\# \\'"
+      let str1 = "'cmd \"arg1\" '\\''arg2'\\'' !%# \\'\\'' \\! \\% \\#'"
+      let str2 = "'cmd \"arg1\" '\\''arg2'\\'' \\!\\%\\# \\'\\'' \\\\! \\\\% \\\\#'"
     endif
-    call assert_equal(str1, shellescape("cmd \"arg1\" 'arg2' !%# \\"), e[0])
-    call assert_equal(str2, shellescape("cmd \"arg1\" 'arg2' !%# \\", 1), e[0])
+    call assert_equal(str1, shellescape("cmd \"arg1\" 'arg2' !%# \\' \\! \\% \\#"), e[0])
+    call assert_equal(str2, shellescape("cmd \"arg1\" 'arg2' !%# \\' \\! \\% \\#", 1), e[0])
 
     " Try running an external command with the shell.
     if executable(e[0])
diff --git a/src/version.c b/src/version.c
index 9f67d79..3a16dda 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3393,
+/**/
     3392,
 /**/
     3391,