abbr: Print optional set-cursor arg correctly

Allows the output to round-trip.

Fixes #11141

src/builtins/abbr.rs

@@ -132,7 +132,7 @@ fn abbr_show(streams: &mut IoStreams) -> Option<c_int> {
         for abbr in abbrs.list() {
             result.clear();
             let mut add_arg = |arg: &wstr| {
-                if !result.is_empty() {
+                if !result.is_empty() && !result.ends_with("=") {
                     result.push_str(" ");
                 }
                 result.push_utfstr(arg);

tests/checks/abbr.fish

@@ -204,3 +204,7 @@ abbr --add regex_name --regex '(*UTF).*' bar
 # CHECKERR: abbr: Regular expression compile error: using UTF is disabled by the application
 # CHECKERR: abbr: (*UTF).*
 # CHECKERR: abbr:      ^
+
+abbr --add foo --set-cursor 'foo % bar'
+abbr | grep foo
+# CHECK: abbr -a --set-cursor='%' -- foo 'foo % bar'