LibGfx/CCITT: Put the code to read the run length in its own function

This is already nice to do for the sole purpose of the readability but
that will also become handy for the 2D decoder.

Userland/Libraries/LibGfx/ImageFormats/CCITTDecoder.cpp

@@ -272,6 +272,36 @@ Color invert(Color current_color)
     return current_color == ccitt_white ? ccitt_black : ccitt_white;
 }
 
+ErrorOr<u32> read_run_length(BigEndianInputBitStream& input_bit_stream, Color current_color, u32 image_width, u32 column)
+{
+    u8 size {};
+    u16 potential_code {};
+    u32 run_length {};
+    while (size < 14) {
+        potential_code <<= 1;
+        potential_code |= TRY(input_bit_stream.read_bit());
+        size++;
+
+        if (auto const maybe_markup = get_markup_code(current_color, potential_code, size); maybe_markup.has_value()) {
+            run_length += maybe_markup->run_length;
+            // OK, let's reset the loop to read a terminal code now
+            size = 0;
+            potential_code = 0;
+        } else if (auto const maybe_terminal = get_terminal_code(current_color, potential_code, size); maybe_terminal.has_value()) {
+            run_length += maybe_terminal->run_length;
+            break;
+        }
+    }
+
+    if (size == 14)
+        return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid CCITT code");
+
+    if (column + run_length > image_width)
+        return Error::from_string_literal("TIFFImageDecoderPlugin: CCITT codes encode for more than a line");
+
+    return run_length;
+}
+
 ErrorOr<void> decode_single_ccitt3_1d_line(BigEndianInputBitStream& input_bit_stream, BigEndianOutputBitStream& decoded_bits, u32 image_width)
 {
     // We always flip the color when entering the loop, so let's initialize the
@@ -291,29 +321,7 @@ ErrorOr<void> decode_single_ccitt3_1d_line(BigEndianInputBitStream& input_bit_st
 
         current_color = invert(current_color);
 
-        u8 size {};
-        u16 potential_code {};
-        while (size < 14) {
-            potential_code <<= 1;
-            potential_code |= TRY(input_bit_stream.read_bit());
-            size++;
-
-            if (auto const maybe_markup = get_markup_code(current_color, potential_code, size); maybe_markup.has_value()) {
-                run_length += maybe_markup->run_length;
-                // OK, let's reset the loop to read a terminal code now
-                size = 0;
-                potential_code = 0;
-            } else if (auto const maybe_terminal = get_terminal_code(current_color, potential_code, size); maybe_terminal.has_value()) {
-                run_length += maybe_terminal->run_length;
-                break;
-            }
-        }
-
-        if (size == 14)
-            return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid CCITT code");
-
-        if (column + run_length > image_width)
-            return Error::from_string_literal("TIFFImageDecoderPlugin: CCITT codes encode for more that a line");
+        run_length += TRY(read_run_length(input_bit_stream, current_color, image_width, column));
     }
 
     TRY(decoded_bits.align_to_byte_boundary());