Fix MP3 VBR Headers (#113)

**Description**: This is basically a rewrite of the VBR header implementation for MP3 files. It offers a much more robust solution for determining duration of MP3s and best efforts at determining MP3 bitrates.

**Testing**: Brand new testing of the VBR headers and MPEG audio headers

---

* Code for reading VBR headers is waaaaay improved. Only thing remaining is taking into consideration encoder delays from sample count

* Incorporate encoder delay/padding from LAME headers

* Incorporate delay for VBRI headers

* Adding sample files

* Working on tests...

* 100% coverage of MpegAudioHeader

* Unit tests for VBRI headers

* Unit tests for VBR headers

* Updating MPEG header to prevent reserved bitrate/audio sample rates from being propagated

* Rollback "allow zero" changes, patch up the rest of the unit tests

* Removing properties tests from mp3 id3vx tests

* Fix MPEG audio stream detection
ALSO UNCOVER A HUGE BUG IN APE FILE INTEGRATION TESTS??? WTF

* Fixing a thing after merging develop

* Enabling one more test

Author: Benjamin Russell

src/combinedTag.ts

@@ -432,8 +432,12 @@ export default abstract class CombinedTag extends Tag {
             if (!t) { return false; }
 
             // Block falsy values (false, 0, null, undefined, NaN), allow ""
-            const val = propertyFn(t);
-            return val || (typeof(val) === "string" &&  val === "");
+            const value = propertyFn(t);
+
+            // @TODO: Just return undefined if the field isn't set... this is a pain
+            return value !== undefined
+                && value !== null
+                && !this.isDefaultValue(value, defaultValue);
         });
         return tagWithProperty ? propertyFn(tagWithProperty) : defaultValue;
     }
@@ -460,5 +464,13 @@ export default abstract class CombinedTag extends Tag {
         }
     }
 
+    private isDefaultValue<T>(value: T, defaultValue: T) {
+        if (Number.isNaN(defaultValue) && Number.isNaN(value)) {
+            return true;
+        }
+
+        return value === defaultValue;
+    }
+
     // #endregion
 }

src/mpeg/mpegAudioFile.ts

@@ -31,15 +31,17 @@ export default class MpegAudioFile extends SandwichFile {
         }
 
         // @TODO: if readStyle is higher than average, scan the entire file to accurately calculate
-        //    the duration.
+        //    the duration and bitrate
 
-        // Skip if we're not reading the properties
-        this._firstHeader = MpegAudioHeader.find(this, this.mediaStartPosition, 0x4000);
+        const searchStart = this.mediaStartPosition;
+        const searchEnd = searchStart + 0x400;
+        const streamLength = this.mediaEndPosition - this.mediaStartPosition;
+
+        this._firstHeader = MpegAudioHeader.fromFile(this, searchStart, searchEnd, streamLength);
         if (!this._firstHeader) {
             throw new CorruptFileError("MPEG audio header not found");
         }
 
-        this._firstHeader.streamLength = this.mediaEndPosition - this.mediaStartPosition;
         return new Properties(this._firstHeader.durationMilliseconds, [this._firstHeader]);
     }
 }