Protect against automatic adding of comma

str2func adds a comma when there is a space in the string. Bug was
detected on an example by Gu Xin
Double check of space before storing

Unwanted space occurs when an equation spans two lines and the first
line ends with an equality sign. It then affects the behavior os
str2func, which adds a comma when there is a space in the string. Bug
was detected on an example by Gu Xin