Fix crash bugs with & entities in <h1> tags

This review fixes an infinite loop when &-entities are found within an <h1> tag.

• Bonus Semantic 0 vs. NULL vs. '\0' changes for readability.
• Reformat functions to be readable; spacing and missing braces.
• Sorry for the whitespace changes. It looks like it was 2-space indented so I stuck with that, but some of these lines were mixed tabs/spaces.