Fix SSH shell arguments and environment handling

[binaryfire]

Summary

Fix ssh2_shell() argument validation and make shell and exec environment handling safe and consistent.

• Accept complete width/height pairs and reject width-only calls with a warning and false.
• Traverse environment keys and values with one paired Zend hash iterator.
• Handle empty shell environment arrays without touching invalid hash state.
• Keep environment values out of setenv failure warnings.

Details

The existing arity check tests five arguments, which rejects a valid width/height call and leaves the incomplete four-argument form unchecked. It also raises E_ERROR, making the documented false return unreachable.

The shell environment loop uses the array's internal pointer, while the exec loop advances an external position for keys but reads values from the internal pointer. Empty shell arrays can reach invalid iterator state, and exec can pair later keys with the wrong value.

Both paths now use ZEND_HASH_FOREACH_STR_KEY_VAL. Numeric keys retain the existing notice behavior. Failed environment requests still identify the variable, but no longer include its value.

Tests

Added PHPT coverage for:

• valid and incomplete shell dimensions;
• empty shell environments;
• paired exec environment iteration;
• shell and exec warning redaction.

The extension builds cleanly, the package manifest validates, and the branch merges cleanly with the other open SSH2 fixes in #102, #103, and #104.