LibCompress: Check for impossible back references in DeflateDecompressor

This commit makes sure that we fail if an encoded lz77 back reference
references bytes that are outside our sliding window, instead of just
silently failing, which triggers an assertion down the line.

Userland/Libraries/LibCompress/Deflate.cpp

@@ -178,6 +178,10 @@ bool DeflateDecompressor::CompressedBlock::try_read_more()
         for (size_t idx = 0; idx < length; ++idx) {
             u8 byte = 0;
             m_decompressor.m_output_stream.read({ &byte, sizeof(byte) }, distance);
+            if (m_decompressor.m_output_stream.handle_any_error()) {
+                m_decompressor.set_fatal_error();
+                return false; // a back reference was requested that was too far back (outside our current sliding window)
+            }
             m_decompressor.m_output_stream << byte;
         }