Scaladoc: Fix emphasis rule in hljs config

[pikinier20]

closes #12868

I've figured out that:

• hljs enters comment parsing mode on /**
• hljs finds * so it enters emphasis mode
• hljs looks for * to exit emphasis mode and it finds * in */
• hljs takes * from */ so it can't exit comment and takes next line as comment

So my solution is to check in begin condition of emphasis mode if the next * char is not followed by / (marks comment end) and * (potentially starts bold mode)

[TheElectronWill]

Nice solution!