Attempt to fallback to a default font, for non-available ones, in more cases (issue 16432)

This essentially extends PR 11218 to also apply when looking up the final font-reference, via the XRef-table, fails because the font isn't available.

This patch also changes `PartialEvaluator.fallbackFontDict` to simply use "Helvetica" as the default font-name, since that seems generally reasonable given the now existing font-substitution code.

src/core/evaluator.js

@@ -1212,26 +1212,7 @@ class PartialEvaluator {
         fontRef = fontRes.getRaw(fontName);
       }
     }
-    if (!fontRef) {
+    if (fontRef) {
-      const partialMsg = `Font "${
-        fontName || (font && font.toString())
-      }" is not available`;
-
-      if (!this.options.ignoreErrors && !this.parsingType3Font) {
-        warn(`${partialMsg}.`);
-        return errorFont();
-      }
-      warn(`${partialMsg} -- attempting to fallback to a default font.`);
-
-      // Falling back to a default font to avoid completely broken rendering,
-      // but note that there're no guarantees that things will look "correct".
-      if (fallbackFontDict) {
-        fontRef = fallbackFontDict;
-      } else {
-        fontRef = PartialEvaluator.fallbackFontDict;
-      }
-    }
-
       if (this.parsingType3Font && this.type3FontRefs.has(fontRef)) {
         return errorFont();
       }
@@ -1241,9 +1222,21 @@ class PartialEvaluator {
       }
 
       font = xref.fetchIfRef(fontRef);
+    }
+
     if (!(font instanceof Dict)) {
+      if (!this.options.ignoreErrors && !this.parsingType3Font) {
+        warn(`Font "${fontName}" is not available.`);
         return errorFont();
       }
+      warn(
+        `Font "${fontName}" is not available -- attempting to fallback to a default font.`
+      );
+
+      // Falling back to a default font to avoid completely broken rendering,
+      // but note that there're no guarantees that things will look "correct".
+      font = fallbackFontDict || PartialEvaluator.fallbackFontDict;
+    }
 
     // We are holding `font.cacheKey` references only for `fontRef`s that
     // are not actually `Ref`s, but rather `Dict`s. See explanation below.
@@ -4412,7 +4405,7 @@ class PartialEvaluator {
 
   static get fallbackFontDict() {
     const dict = new Dict();
-    dict.set("BaseFont", Name.get("PDFJS-FallbackFont"));
+    dict.set("BaseFont", Name.get("Helvetica"));
     dict.set("Type", Name.get("FallbackType"));
     dict.set("Subtype", Name.get("FallbackType"));
     dict.set("Encoding", Name.get("WinAnsiEncoding"));

test/pdfs/issue16432.pdf.link

@@ -0,0 +1 @@
+https://github.com/mozilla/pdf.js/files/11493613/inputFields-Flattened-Output.pdf

test/test_manifest.json

@@ -50,6 +50,14 @@
        "lastPage": 3,
        "type": "eq"
     },
+    {  "id": "issue16432",
+       "file": "pdfs/issue16432.pdf",
+       "md5": "b67b0324c307d8af43d11b0edec88e3e",
+       "rounds": 1,
+       "link": true,
+       "lastPage": 1,
+       "type": "eq"
+    },
     {  "id": "tracemonkey-fbf",
        "file": "pdfs/tracemonkey.pdf",
        "md5": "9a192d8b1a7dc652a19835f6f08098bd",