Replace command with not enough args by an endchar in CFF font

- Right now, a glyph with an erroneous outline is replaced by an empty glyph
    if the error is far enough from the start there's likely something to render
    so the idea is to replace a command with args by an endchar when no args are
    on the stack: this way OTS is likely happy (no remaining args on stack) and we
    can draw something which is likely better than nothing.

test/pdfs/.gitignore

@@ -129,6 +129,7 @@
 !bug1513120_reduced.pdf
 !bug1538111.pdf
 !bug1552113.pdf
+!issue6132.pdf
 !issue9949.pdf
 !bug1308536.pdf
 !bug1337429.pdf

test/test_manifest.json

@@ -2616,6 +2616,12 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "issue6132",
+       "file": "pdfs/issue6132.pdf",
+       "md5": "bd1e6252ca642acf2cd05db1748a073c",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue4875",
        "file": "pdfs/issue4875.pdf",
        "md5": "9a558e18029a42c0ef4e9a8755e24733",