2 bugs fixed:

empty string will be true in conditional expressions,but now it is false(and string that is not empty and is not numerable will be true)

foreach(var i;func(){return []}()); will cause sigsegv because codegen generates error op_pop and op_cntpop,now the counter in_foreach and in_forindex change after generating
foreach/forindex expression before block generation.

nasal_vm.h

@@ -284,7 +284,7 @@ inline bool nasal_vm::condition(nasal_ref val)
     {
         double num=str2num(val.str()->c_str());
         if(std::isnan(num))
-            return val.str()->empty();
+            return !val.str()->empty();
         return num;
     }
     return false;