util: Handle errors from realpath

realpath() can fail and return NULL.  Recent versions of Glibc,
including the one included in Ubuntu 20.04 on ARM, tag realpath
such that the compiler will emit a warning if the return code
is ignored.  In addition to fixing a real issue, this patch
silences an ignored return value warnig.

Signed-off-by: Brian Barrett <bbarrett@amazon.com>

Author: bwbarrett

opal/util/path.c

@@ -393,10 +393,15 @@ char *opal_find_absolute_path(char *app_name)
 
     if (NULL != abs_app_name) {
         char *resolved_path = (char *) malloc(OPAL_PATH_MAX);
-        realpath(abs_app_name, resolved_path);
+        char *ret;
+        ret = realpath(abs_app_name, resolved_path);
         if (abs_app_name != app_name) {
             free(abs_app_name);
         }
+        if (NULL == ret) {
+            free(resolved_path);
+            resolved_path = NULL;
+        }
         return resolved_path;
     }
     return NULL;