processAndStore() computed sizePercent as outputSize/fetchBytes*100
without checking for zero, producing Inf/NaN in logs and metrics.
Also treat empty cached source data the same as missing (re-fetch
from upstream) since zero-byte images can't be processed.
Fixes#5
When a source URL has query parameters, GenerateSignedURL() was
embedding a bare '?' in the path, causing everything after it to be
parsed as the HTTP query string instead of as path segments. This
made the size/format segment unreachable by the URL parser.
Percent-encode the query string in the path segment so it remains
part of the path and can be correctly extracted by ParseImagePath.
Fixes#2
clawbot