[GR-49707] Avoid suffix duplication in the generated image name.

[graalvmbot]

If the name of an image already ends in "suffix", then don't add the suffix again. This avoids "lib.so.so" by default, but still allows it with -o lib.so.so.

no name (no -o) argument:

/home/christian/oracle/cw-examples/jira/GR-49707/test.so (shared_library, 13.00MiB)
/home/christian/oracle/cw-examples/jira/GR-49707/test.h (c_header, 189B)

setting -o lib.so:

 /home/christian/oracle/cw-examples/jira/GR-49707/test.so (shared_library, 13.00MiB)
 /home/christian/oracle/cw-examples/jira/GR-49707/test.so.h (c_header, 195B)

with -o lib.so.so:

 /home/christian/oracle/cw-examples/jira/GR-49707/test.so.so (shared_library, 13.00MiB)
 /home/christian/oracle/cw-examples/jira/GR-49707/test.so.so.h (c_header, 201B)