Ignore non-Stream /SMask-entries when parsing images (issue 14814)

This is similar to the pre-existing check used in the /Mask-case below, to handle *corrupt* PDF documents that include non-Stream /SMask-entries in images; please refer to the PDF specification:
https://web.archive.org/web/20220309040754if_/https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#page=216

*Please note:* Adobe Reader also fails to render the image on the second page, and displays an error message.

test/pdfs/.gitignore

@@ -505,6 +505,7 @@
 !poppler-85140-0.pdf
 !poppler-395-0-fuzzed.pdf
 !GHOSTSCRIPT-698804-1-fuzzed.pdf
+!issue14814.pdf
 !poppler-91414-0-53.pdf
 !poppler-91414-0-54.pdf
 !poppler-742-0-fuzzed.pdf

test/test_manifest.json

@@ -98,6 +98,13 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "issue14814",
+       "file": "pdfs/issue14814.pdf",
+       "md5": "a1c8b677335ff5ea0d07e35e7dffb6e8",
+       "rounds": 1,
+       "firstPage": 2,
+       "type": "eq"
+    },
     {  "id": "issue14269",
        "file": "pdfs/issue14269.pdf",
        "md5": "f34abf77a418f54e13fbcd03b063432e",