crash if PAPI unavailable

[loveshack]

If PAPI isn't available (e.g. in VMs), apart from the error messages at startup, you get a SEGV writing the report at finalization. I fixed that with this change.

--- IPM-2.0.6/src/report_xml.c~	2016-07-17 00:15:01.000000000 +0100
+++ IPM-2.0.6/src/report_xml.c	2019-04-12 15:37:22.087631803 +0100
@@ -293,7 +293,7 @@
 
   nmod=0;
   for( i=0; i<MAXNUM_MODULES; i++ ) {
-    if( !(modules[i].name) || !(modules[i].xml) ) 
+    if( (modules[i].state == STATE_ERROR) || !(modules[i].name) || !(modules[i].xml) ) 
       continue;
 
     nmod++;
@@ -304,7 +304,7 @@
   /* print the contribution to the task-wide <modules> entry
      or the region-specific <modules> entry for each module */
   for( i=0; i<MAXNUM_MODULES; i++ ) {
-    if( !(modules[i].name) || !(modules[i].xml) ) 
+    if( (modules[i].state == STATE_ERROR) || !(modules[i].name) || !(modules[i].xml) ) 
       continue;
 
     res+=modules[i].xml(&(modules[i]), ptr, reg);