Update MultiplyString.java

Submission Result: Compile Error

Line 34: cannot find symbol: variable num12

Runtime error for "0", "0"

Submission Result: Wrong Answer

Input:	"9", "9"
Output:	"8"
Expected:	"81"


Submission Result: Wrong Answer

Input:	"123", "456"
Output:	"15048"
Expected:	"56088"