Fix critical bug in qpms_vecspharm_fill()

Pointer incrementation in wrong cycle, leading to numerically
completely wrong results in most cases.

At higher level, this seems to have affected only plane wave
decompositions.


Former-commit-id: 7ebdb8b8f3f645d76e924b86379172d2c6fac8dc

qpms/vswf.c

@@ -376,9 +376,9 @@ qpms_errno_t qpms_vecspharm_fill(csphvec_t *const a1target, csphvec_t *const a2t
         p3->phic = 0;
         ++p3;
       }
-    }
       ++pleg; ++ppi; ++ptau;
     }
+  }
   qpms_pitau_free(pt);
   return QPMS_SUCCESS;
 }