simplify mw_perl_src_file_cstr to avoid gcc warning

This works around a gcc (Debian 10.2.1-6) warning,
and is less code, even

1 files changed, 1 insertions, 3 deletions

diff --git a/mwrap_core.h b/mwrap_core.h
index 15df857..deb3bb3 100644
--- a/mwrap_core.h
+++ b/mwrap_core.h
@@ -389,10 +389,8 @@ static const char *mw_perl_src_file_cstr(unsigned *lineno)
 {
         const COP *cop = mwp_curcop();
         if (!cop) return NULL;
-        const char *fn = CopFILE(cop);
-        if (!fn) return NULL;
         *lineno = CopLINE(cop);
-        return fn;
+        return CopFILE(cop);
 }
 #        define SRC_FILE_CSTR(lineno) mw_perl_src_file_cstr(lineno)
 #endif /* MWRAP_PERL */