plug a potentially huge memory leak

src/spicelib/devices/vsrc/vsrcdel.c

@@ -7,6 +7,7 @@ Author: 1985 Thomas L. Quarles
 #include "vsrcdefs.h"
 #include "ngspice/sperror.h"
 #include "ngspice/suffix.h"
+#include "ngspice/1-f-code.h"
 
 
 int
@@ -15,8 +16,10 @@ VSRCdelete(GENinstance *gen_inst)
     VSRCinstance *inst = (VSRCinstance *) gen_inst;
 
     FREE(inst->VSRCcoeffs);
-
-    FREE(inst->VSRCtrnoise_state);
+    if (inst->VSRCtrnoise_state) {
+        FREE(inst->VSRCtrnoise_state->oneof);
+        FREE(inst->VSRCtrnoise_state);
+    }
     FREE(inst->VSRCtrrandom_state);
 
     return OK;