src/rrd_fetch_libdbi.c: fix Coverity CID#13634 Logically dead code

src/rrd_fetch_libdbi.c: fix Coverity CID#13634 Logically dead code

        CWE-561 / https://cwe.mitre.org/data/definitions/561.html

        NOTE: this seems like a copy & paste error; either we compare
        'h1' to (char)-1 in which case the code cannot be reached (the
        same test is already done & it returns from the function), or
        (more likely) it should be 'h2' instead.