Fix compiler warning for make static

[michaelortmann]

Found by: michaelortmann
Patch by: michaelortmann
Fixes:

One-line summary:
Fix compiler warning for make static

Additional description (if needed):

Test cases demonstrating functionality (if applicable):
Fixes the following compiler warning:

$ make static
[...]
gcc -g -O2 -pipe -Wall -I.. -I..  -DHAVE_CONFIG_H -I/usr/include -DSTATIC  -c modules.c
modules.c: In function ‘module_load’:
modules.c:698:10: warning: unused variable ‘len’ [-Wunused-variable]
  698 |   size_t len;
      |          ^~~