Code spans at start of line 2nd attempt.

There were two obvious reasons why that was failing. That's what hapens
when I'm in a hurry. Fixed now.

markdown/htmlparser.py

@@ -83,7 +83,7 @@ def at_line_start(self):
         if self.offset > 3:
             return False
         # Confirm up to first 3 chars are whitespace 
-        return self.rawdata[self.line_offset:self.offset].strip() == ''
+        return self.rawdata[self.line_offset:self.line_offset + self.offset].strip() == ''
 
     def handle_starttag(self, tag, attrs):
         self.stack.append(tag)

tests/test_syntax/blocks/test_html_blocks.py

@@ -227,7 +227,6 @@ def test_raw_surrounded_by_text_without_blank_lines(self):
             )
         )
 
-    # TODO: Fix this. Not sure why its failing...
     def test_multiline_markdown_with_code_span(self):
         self.assertMarkdownRenders(
             self.dedent(
@@ -240,8 +239,8 @@ def test_multiline_markdown_with_code_span(self):
             self.dedent(
                 """
                 <p>A paragraph with a block-level
-                <code>&lt;p&gt;code span&lt;/p&gt;</code>.
-                More <em>Markdown</em> text.</p>
+                <code>&lt;p&gt;code span&lt;/p&gt;</code>, which is
+                at the start of a line.</p>
                 """
             )
         )