Implicit conversion warnings

[rettinghaus]

There are some newer compiler warnings about implicit conversions:

/min/humlib.cpp:5826:64 Implicit conversion loses integer precision: 'size_type' (aka 'unsigned long') to 'result_type' (aka 'int')
/min/humlib.cpp:27843:22 Implicit conversion loses integer precision: 'size_type' (aka 'unsigned long') to 'int'
/min/humlib.cpp:122606:29 Implicit conversion loses integer precision: 'size_type' (aka 'unsigned long') to 'int'
/min/humlib.cpp:123119:24 Implicit conversion loses integer precision: 'size_type' (aka 'unsigned long') to 'int'
/min/humlib.cpp:123217:28 Implicit conversion loses integer precision: 'size_type' (aka 'unsigned long') to 'int'

(Based on the current version in Verovio.)