Remove the contents of libjasper_compat.c.  The assignment

        *errorP  = errorP;

is bogus because it creates a non-null value in *errorP even on
success, and the caller expects a null pointer int his case.

The source file is compiled, but not actually linked in, so this is
only a problem because of the type error that fails the build.

diff --git a/converter/other/jpeg2000/libjasper_compat.c b/converter/other/jpeg2000/libjasper_compat.c
index 101820a321212dc6..e69de29bb2d1d643 100644
--- a/converter/other/jpeg2000/libjasper_compat.c
+++ b/converter/other/jpeg2000/libjasper_compat.c
@@ -1,26 +0,0 @@
-#include "netpbm/nstring.h"
-
-#include "jasper/jasper.h"
-#include "jasper/jas_image.h"
-
-#ifndef JAS_HAVE_PMJAS_IMAGE_DECODE
-
-void
-pmjas_image_decode(jas_stream_t * const in,
-                   int            const fmtArg,
-                   const char *   const optstr,
-                   jas_image_t ** const imagePP,
-                   const char **  const errorP) {
-
-    jas_image_t * const jasperP = jas_image_decode(in, fmtArg, optstr);
-
-    if (jasperP) {
-        *imagePP = jasperP;
-        *errorP  = errorP;
-    } else {
-        pm_asprintf(errorP, "Failed.  Details may have been written to "
-                    "Standard Error");
-    }
-}
-
-#endif