env: micro-optimization

env: micro-optimization
printenv: fix "printenv VAR1 VAR2" bug (wasn't printing VAR2)
(spotted by kalyanatejaswi balabhadrapatruni <kalyanatejaswi@yahoo.co.in>)

env_main                                             267     260      -7
printenv_main                                        147      75     -72
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-79)             Total: -79 bytes
   text    data     bss     dec     hex filename
 770336    1096   11228  782660   bf144 busybox_old
 770256    1096   11228  782580   bf0f4 busybox_unstripped