Correctly break during Png decoding

[JimBobSquarePants]

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Description

Fixes #2752

We weren't breaking from the loop only the nested switch. We were also missing a chunk break. The first fcTL chunk in a PNG is followed by one or more IDAT chunk, only subsequent fcTL chunks are followed by fdAT chunks.

The test image contains the following chunks.

IHDR, pHYs, acTL, fcTL, IDAT ×3, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT,
fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, 
fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT,
fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT,
fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL,
fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT,
fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, fcTL, fdAT, fdAT, IEND

[brianpopow]

looks good now