bug fix rvalue

Bug that tried to assign an rvalue to and lvalue reference. MSVC compiler did not care at the time. Compiler probably got updated and is now up to the c++ standard.

See here:

• https://stackoverflow.com/questions/53136307/msvc-binds-non-const-lvalue-reference-to-an-rvalue-temporary
• https://stackoverflow.com/questions/7189420/one-vs2010-bug-allowing-binding-non-const-reference-to-rvalue-without-even-a-w?rq=4

(Delete branch on merge??)