Block decomposition: bugfix with temporary terms when mfs=3

In an “evaluate” block, the LHS of a renormalized equation (such as “log(x)=…”)
could be associated to a temporary term that would then be incorrectly
computed: that temporary term would be evaluated *before* (and not after) the
evaluation of the associated variable (“x” in the example).

(cherry picked from commit 627dd92c)