Address several issues reported by cppcheck all over the place.

* src/bin/common_finput.cc, src/tgbaalgos/lbtt.cc: Use !empty() instead
of size() > 0.
* src/bin/ltl2tgta.cc, src/kripke/kripkeexplicit.cc,
src/tgbatest/complementation.cc: Avoid useless assignments.
* src/bin/ltlcross.cc: Correct mistaken assignment inside assert().
* src/evtgba/symbol.hh, src/tgba/tgbabddcoredata.cc,
src/tgba/tgbabddcoredata.hh,
src/tgba/tgbasafracomplement.cc (operator=): Do not return a const
reference.
* src/evtgbatest/ltl2evtgba.cc, src/evtgbatest/product.cc,
src/evtgbatest/product.cc: Check indices before using them, not after.
* src/kripke/kripkeexplicit.cc, src/kripke/kripkeexplicit.hh,
src/tgbatest/randtgba.cc: Pass constant strings by reference.
* src/kripke/kripkeprint.cc, src/tgbaalgos/simulation.cc:
Remove a useless operation.
* src/ltlvisit/simplify.cc: Remove a duplicate condition.
* src/misc/formater.hh: Remove unused attribute.
* src/misc/modgray.cc: Initialize done_ in the constructor.
* src/saba/explicitstateconjunction.cc,
src/saba/explicitstateconjunction.hh (operator=): Fix prototype.
* src/saba/sabacomplementtgba.cc: Remove unused default constructor.
* src/ta/taexplicit.cc, src/ta/taproduct.cc, src/ta/tgtaproduct.cc,
src/ta/tgtaproduct.hh, src/taalgos/emptinessta.cc,
src/taalgos/minimize.cc, src/taalgos/reachiter.cc,
src/taalgos/tgba2ta.cc, src/tgbaalgos/cutscc.cc: Use C++ casts, and
++it instead of it++.
* src/taalgos/dotty.cc, src/tgbatest/ltl2tgba.cc: Refine the scope of
variables.
* src/tgba/tgbakvcomplement.hh (bdd_order): Always initialize bdd_.
* src/tgba/tgbasgba.cc, src/tgba/wdbacomp.cc: Use the initialization
line to initialize all members.

src/taalgos/minimize.cc

@@ -205,7 +205,7 @@ namespace spot
 
     spot::state* artificial_initial_state = ta_->get_artificial_initial_state();
 
-    for (it = states_set.begin(); it != states_set.end(); it++)
+    for (it = states_set.begin(); it != states_set.end(); ++it)
       {
         const state* s = (*it);