#8 charge parser doesn't check input

[Andrew Dalke]

The parser code for the charge layer doesn't check the input repeat count, so this

InChI=1/C/q2987987*-1

writes a lot of "-1"s to the heap, almost certainly causing a segmentation fault, or corrupting data.

Also, the underlying code uses atoi to parse the string so I can give it a negative number. I can't overflow the data structure in the other direction but I can use it to jump backwards.

For a neat example, this one backs up and replaces already assigned charges.

InChI=1/C.O/q2*-1;-2*+1;+3;+4

when passed to the InChI code produces

InChI=1/C.O/q+3;+4

The code should verify that the repeat counts are > 0 and never exceed the number of components.