Fix error messages so we don't output an extra line

Before this commit, when a file ended with a newline, the syntax error
message would show an extra line after the file.

For example, the error message would look like this:

```
[aaron@tc-lan-adapter ~/g/ruby (master)]$ echo "foo(" > test.rb
[aaron@tc-lan-adapter ~/g/ruby (master)]$ od -c test.rb
0000000    f   o   o   (  \n
0000005
[aaron@tc-lan-adapter ~/g/ruby (master)]$ wc -l test.rb
       1 test.rb
[aaron@tc-lan-adapter ~/g/ruby (master)]$ ./miniruby test.rb
test.rb: test.rb:1: syntax error found (SyntaxError)
> 1 | foo(
    |     ^ unexpected end-of-input; expected a `)` to close the arguments
  2 |
```

This commit fixes the "end of line" book keeping when printing an error
so that there is no extra line output at the end of the file:

```
[aaron@tc-lan-adapter ~/g/ruby (fix-last-line-error)]$ echo "foo(" | ./miniruby
-: -:1: syntax error found (SyntaxError)
> 1 | foo(
    |     ^ unexpected end-of-input; expected a `)` to close the arguments

[aaron@tc-lan-adapter ~/g/ruby (fix-last-line-error)]$ echo -n "foo(" | ./miniruby
-: -:1: syntax error found (SyntaxError)
> 1 | foo(
    |     ^ unexpected end-of-input; expected a `)` to close the arguments

```

Notice that in the above example, the error message only displays one
line regardless of whether or not the file ended with a newline.

[Bug #20918]
[ruby-core:120035]

prism_compile.c

@@ -10444,7 +10444,20 @@ pm_parse_errors_format(const pm_parser_t *parser, const pm_list_t *error_list, p
         // Here we determine how many lines of padding to display after the
         // error, depending on where the next error is in source.
         last_line = error->line;
-        int32_t next_line = (index == error_list->size - 1) ? (((int32_t) newline_list->size) + parser->start_line) : errors[index + 1].line;
+        int32_t next_line;
+
+        if (index == error_list->size - 1) {
+            next_line = (((int32_t) newline_list->size) + parser->start_line);
+
+            // If the file ends with a newline, subtract one from our "next_line"
+            // so that we don't output an extra line at the end of the file
+            if ((parser->start + newline_list->offsets[newline_list->size - 1]) == parser->end) {
+                next_line--;
+            }
+        }
+        else {
+            next_line = errors[index + 1].line;
+        }
 
         if (next_line - last_line > 1) {
             pm_buffer_append_string(buffer, "  ", 2);