_zoneinfo: reject empty quoted POSIX TZ abbreviations (#9017)

* Reject empty quoted POSIX timezone abbreviations

Split the Python 3.14-compatible parser guard from #8954. Cover empty standard and daylight-saving abbreviations and preserve valid quoted names.

Assisted-by: OpenAI Codex:model identifier unavailable

* Keep zoneinfo regression in module snippet

Rename the snippet as requested during review without changing test contents.

Assisted-by: OpenAI Codex:model identifier unavailable

crates/stdlib/src/_zoneinfo.rs

@@ -552,6 +552,9 @@ mod _zoneinfo {
                 parser.bump();
             }
             let end = parser.i;
+            if end == start {
+                return None;
+            }
             parser.bump();
             return Some(String::from_utf8_lossy(&parser.bytes[start..end]).into_owned());
         }

extra_tests/snippets/stdlib_zoneinfo.py

@@ -0,0 +1,19 @@
+import io
+import struct
+from zoneinfo import ZoneInfo
+
+from testutils import assert_raises
+
+# Minimal TZif v3 data with no transitions and a POSIX rule in the footer.
+header = (b"TZif3" + b"\0" * 15 + struct.pack(">6l", 0, 0, 0, 0, 0, 0)) * 2
+
+
+def zone_from_rule(rule):
+    return ZoneInfo.from_file(io.BytesIO(header + b"\n" + rule + b"\n"))
+
+
+for rule in (b"<>5", b"AAA4<>,M3.2.0/2,M11.1.0/3"):
+    assert_raises(ValueError, zone_from_rule, rule)
+
+# Quoting still permits nonempty numeric abbreviations.
+assert zone_from_rule(b"<+05>-5").tzname(None) == "+05"