[fpc-pascal] Bug 37080 -- StrToHostAddr accepts all Pascal number notations

[Noel Duffy]

While doing some work on bug 37060, the refactoring of StrToHostAddr and 
StrToHostAddr6 in the sockets 
unit,(https://bugs.freepascal.org/view.php?id=37060), I found that 
StrToHostAddr is doing no validation at all on input address characters 
before calling the function Val, so any Pascal notation that Val 
accepts, such as 0x and $ for hexadecimal, % for binary, & for octal, 
and mathematical signs are all accepted in ipv4 octets.

https://bugs.freepascal.org/view.php?id=37080

As a consequence, StrToHostAddr will happily parse addresses like these:

0xa.3.4.5
9.$c.4.5
%1111.%11001110.30.4
&7.&5.30.4
12.+4.1.1

Any number in any notation will be accepted as long as byte overflow 
isn't triggered. Thus, + in octets is accepted, but - is not, because 
the function detects that the octet is negative which then triggers 
overflow.

Fixing this is outside the scope of the patch I'm preparing for 37060, 
but if no-one else feels inclined to look into this by the time I'm 
finished with that patch then I'll submit a new patch for it.