[ASM] Avoid exceptions when reading body

[NachoEchevarria]

Summary of changes

Some HttpRequestValidationException have been thrown when reading the request body, which prevents us from processing a particular request that contains dangerous values. This exception is thrown under .net framework when a dangerous body is detected and the request's validation is enabled.

We already were handling this situation when reading body values, but calling Request.Form itselft can also throw this exception, so we just need to cover that part of the code.

Reason for change

Implementation details

Test coverage

Other details