Line-bond structures appear to imply that there are two different isomers of 1,2-dibromobenzene, one with the bromine

Question:

Line-bond structures appear to imply that there are two different isomers of 1,2-dibromobenzene, one with the bromine bearing carbon atoms joined by a double bond and one with the bromine-bearing carbons joined by a single bond. In fact, though, there is only one 1,2 dibromobenzene. Explain.