URL sanitation and validation to prevent XSS

The post prefix url was not properly sanitised and validated.

This vulnerability affects the following application versions:

• All in One SEO Pack 2.3.5
• All in One SEO Pack 2.3.5.1
• All in One SEO Pack 2.3.6
• All in One SEO Pack 2.3.6.1
• All in One SEO Pack 2.3.7
• All in One SEO Pack 2.3.8
• All in One SEO Pack 2.3.9
• All in One SEO Pack 2.3.9.1
• All in One SEO Pack 2.3.9.2
• All in One SEO Pack 2.3.10
• All in One SEO Pack 2.3.10.1
• All in One SEO Pack 2.3.10.2
• All in One SEO Pack 2.3.11
• All in One SEO Pack 2.3.11.1
• All in One SEO Pack 2.3.11.2
• All in One SEO Pack 2.3.11.3
• All in One SEO Pack 2.3.11.4
• All in One SEO Pack 2.3.12
• All in One SEO Pack 2.3.12.1
• All in One SEO Pack 2.3.12.2
• All in One SEO Pack 2.3.12.2.1
• All in One SEO Pack 2.3.12.3
• All in One SEO Pack 2.3.12.4
• All in One SEO Pack 2.3.12.5
• All in One SEO Pack 2.3.13
• All in One SEO Pack 2.3.13.1
• All in One SEO Pack 2.3.13.2
• All in One SEO Pack 2.3.14
• All in One SEO Pack 2.3.14.1
• All in One SEO Pack 2.3.14.2
• All in One SEO Pack 2.3.15
• All in One SEO Pack 2.3.15.1
• All in One SEO Pack 2.3.15.2
• All in One SEO Pack 2.3.15.3
• All in One SEO Pack 2.3.16
• All in One SEO Pack 2.4
• All in One SEO Pack 2.4.1
• All in One SEO Pack 2.4.1.1
• All in One SEO Pack 2.4.2
• All in One SEO Pack 2.4.2.1
• All in One SEO Pack 2.4.3
• All in One SEO Pack 2.4.3.1
• All in One SEO Pack 2.4.4
• All in One SEO Pack 2.4.4.1
• All in One SEO Pack 2.4.5
• All in One SEO Pack 2.4.5.1
• All in One SEO Pack 2.4.6
• All in One SEO Pack 2.4.6.1
• All in One SEO Pack 2.5
• All in One SEO Pack 2.6.1
• All in One SEO Pack 2.7.2
• All in One SEO Pack 2.7.3