glide load gif never loop with LOOP_INTRINSIC mode

[Letty-Liang]

here i find a bug, when glide load git with LOOP_INTRINSIC mode, a forever loop gif will never loop at all

=====code====
in third party parse
https://gist.githubusercontent.com/devunwired/4479231/raw/df2725be4ae0f12f5265deaf0a769936ea94950b/GifDecoder.java
protected int loopCount = 1; // iterations; 0 = repeat forever

/**
 * Reads Netscape extension to obtain iteration count.
 */
private void readNetscapeExt() {
    do {
        readBlock();
        if (block[0] == 1) {
            // Loop count sub-block.
            int b1 = ((int) block[1]) & 0xff;
            int b2 = ((int) block[2]) & 0xff;
            header.loopCount = (b2 << 8) | b1;
        }
    } while ((blockSize > 0) && !err());
}

while in glide loopCount = 0 means never loop

@Override
public void setLoopCount(int loopCount) {
    if (loopCount <= 0 && loopCount != LOOP_FOREVER && loopCount != LOOP_INTRINSIC) {
        throw new IllegalArgumentException("Loop count must be greater than 0, or equal to "
                + "GlideDrawable.LOOP_FOREVER, or equal to GlideDrawable.LOOP_INTRINSIC");
    }

    if (loopCount == LOOP_INTRINSIC) {
        maxLoopCount = decoder.getLoopCount();
    } else {
        maxLoopCount = loopCount;
    }
}

hope u will fix it soon or maybe i could create a pr

[TWiStErRob]

Fixed for 3.8.0 in #1813, you can consume it via https://github.com/bumptech/glide/wiki/Snapshots, thanks @toyama-sumio!