crash when modulating i/o range attributes too quickly

[isabelgk]

Process 91324 stopped
* thread #73, name = 'MacBook Pro Speakers', stop reason = hit program assert
    frame #4: 0x0000000133d2be48 ease~`ease_base<ease>::apply_easing_function(this=0x0000000137259740, input=0.31759637188225304) at ease_base.h:100:3
   97  			const numbers& input_range  = this->input_range;
   98  			const numbers& output_range = this->output_range;
   99
-> 100 			assert(input_range.size() == 2);
   101 			assert(output_range.size() == 2);
   102
   103 			number diff  = (input_range[1] - input_range[0]);