Avoid matching on byte strings

This match didn't compile to efficient code (rust-lang/rust#110870). In
the release build, this commit changes

  10908:       49 8d 54 24 04          lea    0x4(%r12),%rdx
  1090d:       80 3a 70                cmpb   $0x70,(%rdx)
  10910:       0f 85 2a 01 00 00       jne    10a40
  10916:       41 80 7c 24 05 73       cmpb   $0x73,0x5(%r12)
  1091c:       0f 85 1e 01 00 00       jne    10a40
  10922:       41 80 7c 24 06 73       cmpb   $0x73,0x6(%r12)
  10928:       0f 85 12 01 00 00       jne    10a40
  1092e:       41 80 7c 24 07 68       cmpb   $0x68,0x7(%r12)
  10934:       0f 85 06 01 00 00       jne    10a40

to

  108bb:       49 8d 5c 24 04          lea    0x4(%r12),%rbx
  <...>
  10975:       81 3b 70 73 73 68       cmpl   $0x68737370,(%rbx)
  1097b:       0f 84 af 02 00 00       je     10c30

Author: tchebb

src/init_data.rs

@@ -104,16 +104,16 @@ fn parse_cenc(boxes: &[u8]) -> Result<&[u8], InitDataError> {
         };
         let box_payload = checked_slice(remaining, payload_start..payload_end)?;
 
-        match box_type {
-            b"pssh" => {
-                if let Some(wv_pssh) = parse_pssh_box(box_payload)? {
-                    return Ok(wv_pssh);
-                }
-            }
-            _ => warn!(
+        if box_type != b"pssh" {
+            warn!(
                 "Skipping unknown CENC box type: {}",
                 box_type.escape_ascii()
-            ),
+            );
+            continue;
+        }
+
+        if let Some(wv_pssh) = parse_pssh_box(box_payload)? {
+            return Ok(wv_pssh);
         }
 
         remaining = &remaining[payload_end..];