trivial optimization in src/file.c::panel_operate()

[slavazanko]

Message from maillist.

From: Denys Vlasenko (vda).

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I noticed an incorrectly indented if() in file.c::panel_operate().
Took a better look, and found out it can be tweaked in several ways.

This patch is the result.

It contains the following trivial optimizations:

• merged two identical "dest_dir_ = g_strdup (dest_dir)" ops.
• simplified check for trailing '/' (no need to strcmp 1-char string).
• since g_free (NULL) is safe, merged two separate "if empty string then bail out" code paths.
• fixed wording in a comment.

[slavazanko]

created branch 415_trivial_optimization (parent: master)

initial changeset:df256dbaf6521263108958666cda9ac4c3b15608

Review.

[slavazanko]

changeset:3ce5fb127b8c46f2d53ca4cab9ce8e8ae324e11e