Don't map glyphs to unicode non breaking space.

src/core/fonts.js

@@ -2679,6 +2679,7 @@ var Font = (function FontClosure() {
            fontCharCode <= 0x1f || // Control chars
            fontCharCode === 0x7F || // Control char
            fontCharCode === 0xAD || // Soft hyphen
+           fontCharCode === 0xA0 || // Non breaking space
            (fontCharCode >= 0x80 && fontCharCode <= 0x9F) || // Control chars
            // Prevent drawing characters in the specials unicode block.
            (fontCharCode >= 0xFFF0 && fontCharCode <= 0xFFFF) ||

test/test_manifest.json

@@ -592,6 +592,14 @@
        "type": "eq",
        "about": "Glyph accent drawn as curves."
     },
+    {  "id": "issue5138",
+       "file": "pdfs/issue5138.pdf",
+       "md5": "9931686d7dee0df62640fbf58bed3323",
+       "link": false,
+       "rounds": 1,
+       "type": "eq",
+       "about": "Glyph that gets mapped to unicode non-breaking-space."
+    },
     {  "id": "simpletype3font",
        "file": "pdfs/simpletype3font.pdf",
        "md5": "b374c7543920840c61999e9e86939f99",