Keep the first /Subrs and /CharStrings block

Some Type1 fonts (the embedded Optima variants in orw1972.pdf) ship
two /Subrs and /CharStrings blocks wrapped in save/restore frames
gated on an Adobe hires/lores runtime switch.
In such cases, we just use the first /Subrs and /CharStrings block,
which is the one that is actually used by the font renderer in Acrobat.

It fixes #18548.

src/core/type1_parser.js

@@ -566,6 +566,13 @@ class Type1Parser {
       },
     };
     let token, length, data, lenIV;
+    // Some fonts (e.g. those embedded in issue18548.pdf) define a second
+    // `/Subrs` and `/CharStrings` block that the PostScript runtime selects
+    // conditionally (e.g. high-resolution variants). Testing with other
+    // viewers shows that none of them actually use these conditional blocks,
+    // so we can "safely" ignore them.
+    let subrsParsed = false;
+    let charStringsParsed = false;
     while ((token = this.getToken()) !== null) {
       if (token !== "/") {
         continue;
@@ -573,6 +580,10 @@ class Type1Parser {
       token = this.getToken();
       switch (token) {
         case "CharStrings":
+          if (charStringsParsed) {
+            break;
+          }
+          charStringsParsed = true;
           // The number immediately following CharStrings must be greater or
           // equal to the number of CharStrings.
           this.getToken();
@@ -610,6 +621,10 @@ class Type1Parser {
           }
           break;
         case "Subrs":
+          if (subrsParsed) {
+            break;
+          }
+          subrsParsed = true;
           this.readInt(); // num
           this.getToken(); // read in 'array'
           while (this.getToken() === "dup") {

test/pdfs/.gitignore

@@ -922,3 +922,4 @@
 !knockout_groups_test.pdf
 !issue18032.pdf
 !Embedded_font.pdf
+!issue18548_reduced.pdf

test/test_manifest.json

@@ -14267,5 +14267,12 @@
     "md5": "b68dd5a3e6833d1af94e295fe1d60285",
     "rounds": 1,
     "type": "eq"
+  },
+  {
+    "id": "issue18548_reduced",
+    "file": "pdfs/issue18548_reduced.pdf",
+    "md5": "39d15f7f810bd89a4e5858df9c75ca4e",
+    "rounds": 1,
+    "type": "eq"
   }
 ]