Add "break"s to make it clearer what will happen in a nested switch.

This could only matter if the guessed_type variable had a value that wasn't
a member of the PasswordType enum; but just in case, let's be sure that
control falls out to reach the elog(ERROR) at the end of the function.
Per gripe from Coverity.

src/backend/libpq/crypt.c

@@ -162,6 +162,7 @@ encrypt_password(PasswordType target_type, const char *role,
 				case PASSWORD_TYPE_MD5:
 					return pstrdup(password);
 			}
+			break;
 
 		case PASSWORD_TYPE_SCRAM:
 			switch (guessed_type)
@@ -178,6 +179,7 @@ encrypt_password(PasswordType target_type, const char *role,
 				case PASSWORD_TYPE_SCRAM:
 					return pstrdup(password);
 			}
+			break;
 	}
 
 	/*