LibPDF: Do not crash on invalid page drawing operators

Lets us no longer crash rendering page 2 of
BCM2837-ARM-Peripherals.-.Revised.-.V2-1.pdf.

Test file hand-written (based on text.pdf) and offsets fixed up
with `mutool clean` as usual.

Tests/LibPDF/CMakeLists.txt

@@ -14,6 +14,7 @@ set(TEST_FILES
     encoding.pdf
     encryption_nocopy.pdf
     group.pdf
+    invalid-operator.pdf
     jbig2-globals.pdf
     jbig2-globals-indirect-reference.pdf
     jpeg2000-indexed-small.pdf

Tests/LibPDF/TestPDF.cpp

@@ -141,6 +141,20 @@ TEST_CASE(resolve_indirect_reference_during_parsing)
     EXPECT_EQ(jbig2_stream->bytes().size(), 20'000U);
 }
 
+TEST_CASE(invalid_operator)
+{
+    auto file = TRY_OR_FAIL(Core::MappedFile::map("invalid-operator.pdf"sv));
+    auto document = MUST(PDF::Document::create(file->bytes()));
+    MUST(document->initialize());
+    EXPECT_EQ(document->get_page_count(), 1U);
+
+    auto page = MUST(document->get_page(0));
+    auto page_size = Gfx::IntSize { 612, 792 };
+    auto bitmap = TRY_OR_FAIL(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRx8888, page_size));
+    auto result = PDF::Renderer::render(document, page, bitmap, Color::White, PDF::RenderingPreferences {});
+    // Shouldn't crash.
+}
+
 TEST_CASE(jbig2_embedded_organization_cross_chunk_reference)
 {
     auto file = TRY_OR_FAIL(Core::MappedFile::map("jbig2-globals.pdf"sv));

Tests/LibPDF/invalid-operator.pdf

@@ -0,0 +1,37 @@
+%PDF-1.3
+%µ¶
+
+1 0 obj
+<</Type/Catalog/Pages 2 0 R>>
+endobj
+
+2 0 obj
+<</Type/Pages/Kids[3 0 R]/Count 1>>
+endobj
+
+3 0 obj
+<</Type/Page/Parent 2 0 R/MediaBox[0 0 525 250]/Contents 4 0 R>>
+endobj
+
+4 0 obj
+<</Length 5>>
+stream
+q
+QQ
+
+endstream
+endobj
+
+xref
+0 5
+0000000000 65536 f 
+0000000016 00000 n 
+0000000062 00000 n 
+0000000114 00000 n 
+0000000195 00000 n 
+
+trailer
+<</Size 5/Root 1 0 R>>
+startxref
+248
+%%EOF

Userland/Libraries/LibPDF/Operator.h

@@ -96,7 +96,7 @@ enum class OperatorType {
 
 class Operator {
 public:
-    static OperatorType operator_type_from_symbol(StringView symbol_string)
+    static Optional<OperatorType> operator_type_from_symbol(StringView symbol_string)
     {
 #define V(name, snake_name, symbol) \
     if (symbol_string == #symbol)   \
@@ -109,8 +109,7 @@ public:
         if (symbol_string == "\"")
             return OperatorType::TextNextLineShowStringSetSpacing;
 
-        dbgln("unsupported graphics symbol {}", symbol_string);
-        VERIFY_NOT_REACHED();
+        return {};
     }
 
     static char const* operator_name(OperatorType operator_type)

Userland/Libraries/LibPDF/Parser.cpp

@@ -596,7 +596,10 @@ PDFErrorOr<Vector<Operator>> Parser::parse_operators()
             auto operator_string = StringView(m_reader.bytes().slice(operator_start, m_reader.offset() - operator_start));
             m_reader.consume_whitespace();
 
-            auto operator_type = Operator::operator_type_from_symbol(operator_string);
+            auto maybe_operator_type = Operator::operator_type_from_symbol(operator_string);
+            if (!maybe_operator_type.has_value())
+                return error(ByteString::formatted("unsupported operator {}", operator_string));
+            auto operator_type = maybe_operator_type.release_value();
 
             if (operator_type == OperatorType::InlineImageBegin) {
                 if (!operator_args.is_empty())