Fix putImage mutating the global filters array

[douglasmatheus]

Problem

putImage calls splice() on the array returned by getFilters() to remove "FlateEncode" before writing image data. But getFilters() returns the live reference to the document's internal filters array, not a copy:

https://github.com/parallax/jsPDF/blob/master/src/jspdf.js#L1748-L1750

var getFilters = (API.__private__.getFilters = function() {
  return filters;
});

So the splice in putImage permanently empties the document's filters array. After the first image is rendered, all subsequent page content streams are emitted without compression.

Symptoms

Calling doc.output() twice in a row on a document containing any image produces PDFs of dramatically different sizes:

const doc = new jsPDF({ compress: true });
doc.addImage(jpg, "JPEG", 10, 10, 100, 75);

const a = doc.output();
const b = doc.output();

console.log(a.length, b.length);
// → 5440, 110xxx   (page content stream goes from FlateEncoded ~5KB to raw ~100KB)

The first output is correct; every output after that has uncompressed page content streams. The PDF still renders fine in viewers, just much larger than expected.

Cause

src/modules/addimage.js line 206-208:

var filter = getFilters();
while (filter.indexOf("FlateEncode") !== -1) {
  filter.splice(filter.indexOf("FlateEncode"), 1);
}

Since filter and the document's internal filters are the same array reference, the splice strips "FlateEncode" from the document-wide configuration.

Fix

One-line change: copy the array before mutating.

var filter = getFilters().slice();

putImage still gets its local "filters minus FlateEncode" list, and the document's filters array is unaffected.

Test

Added a regression test in test/specs/addimage.spec.js that asserts repeated doc.output() calls return identical buffers. All 541 unit tests pass locally.

Notes

• I did not regenerate dist/ per the CONTRIBUTING guideline.
• Discovered while debugging cumulative PDF growth in a library that wraps jsPDF for canvas-editor-pdf. Happy to add more context if useful.