Fixed bug that added a superfluous empty slot for data when encoding an empty string coming from storage.

Added tests covering empty string, uninitialized string, emptry string literal, byte arrays and explicit call to `abi.encode`.

libsolidity/codegen/ABIFunctions.cpp

@@ -699,7 +699,7 @@ string ABIFunctions::abiEncodingFunctionCompactStorageArray(
 					case 0 {
 						// short byte array
 						mstore(pos, and(slotValue, not(0xff)))
-						ret := add(pos, <lengthPaddedShort>)
+						ret := add(pos, mul(<lengthPaddedShort>, iszero(iszero(length))))
 					}
 					case 1 {
 						// long byte array