Correctly parse ISO 8601 offset

Previously, the minute was effectively required. This goes against the
specification.

tests/parsing.rs

@@ -556,6 +556,7 @@ fn iso_8601() {
         OffsetDateTime::parse("20210102T0304Z", &Iso8601::DEFAULT),
         Ok(datetime!(2021-01-02 03:04:00 UTC))
     );
+    assert_eq!(UtcOffset::parse("+07", &Iso8601::DEFAULT), Ok(offset!(+7)));
     assert_eq!(
         UtcOffset::parse("+0304", &Iso8601::DEFAULT),
         Ok(offset!(+03:04))

time/src/parsing/iso8601.rs

@@ -271,17 +271,23 @@ impl<const CONFIG: EncodedConfig> Iso8601<CONFIG> {
                 };
             }
 
-            let input = min(input)
-                .and_then(|parsed_item| {
-                    parsed_item.consume_value(|min| {
-                        parsed.set_offset_minute_signed(if sign == b'-' {
+            match min(input) {
+                Some(ParsedItem(new_input, min)) => {
+                    input = new_input;
+                    parsed
+                        .set_offset_minute_signed(if sign == b'-' {
                             -(min as i8)
                         } else {
                             min as _
                         })
-                    })
-                })
-                .ok_or(InvalidComponent("offset minute"))?;
+                        .ok_or(InvalidComponent("offset minute"))?;
+                }
+                None => {
+                    // Omitted offset minute is assumed to be zero.
+                    parsed.set_offset_minute_signed(0);
+                }
+            }
+
             // If `:` was present, the format has already been set to extended. As such, this call
             // will do nothing in that case. If there wasn't `:` but minutes were
             // present, we know it's the basic format. Do not use `?` on the call, as