Explicitly zero out persona bitfields

Personae have a flag and a species bitfield. They're built up during parsing, but never explicitly zeroed out. This leads to ships occasionally getting an incorrect persona (especially common with support ships, which never have an explicit persona).

Additionally, this commit addresses an issue with the UES Aranyaka (and potentially other support ships belonging to species without a support persona). I'm honestly not sure why they were ever able to speak; however, with this change, they'll never be able to. As such, this commit introduces a "default support persona" to retain the desired behavior.

Author: naomimyselfandi

code/mission/missionmessage.cpp

@@ -141,7 +141,7 @@ const char *Persona_type_names[MAX_PERSONA_TYPES] =
 //XSTR:ON
 };
 
-int Default_command_persona;
+int Default_command_persona, Default_support_persona;
 
 // Goober5000
 // NOTE - these are truncated filenames, i.e. without extensions
@@ -202,6 +202,8 @@ int comm_between_player_and_ship(int other_shipnum, bool for_death_scream);
 void persona_parse()
 {
 	Persona this_persona;
+	this_persona.flags = 0;
+	this_persona.species_bitfield = 0;
 
 	required_string("$Persona:");
 	stuff_string(this_persona.name, F_NAME, NAME_LENGTH);
@@ -273,13 +275,16 @@ void persona_parse()
 	}
 
 	if (!dup) {
+		int persona_index = (int) Personas.size();
 		Personas.push_back(this_persona);
 
-		// save the Command persona in a global
+		// Save some important personae for later
 		if (this_persona.flags & PERSONA_FLAG_COMMAND) {
-			// always use the most recent Command persona
-			// found, since that's how retail does it
-			Default_command_persona = ((int)Personas.size() - 1);
+			// Always use the most recent Command persona found, since that's how retail does it
+			Default_command_persona = persona_index;
+		}
+		if ((this_persona.flags & PERSONA_FLAG_SUPPORT) && (Default_support_persona == -1)) {
+			Default_support_persona = persona_index;
 		}
 	}
 }
@@ -735,6 +740,7 @@ void messages_init()
 
 	if ( !table_read ) {
 		Default_command_persona = -1;
+		Default_support_persona = -1;
 
 		// speed things up a little by setting the capacities for the message vectors to roughly the FS2 amounts
 		Messages.reserve(500);
@@ -1969,14 +1975,18 @@ int pick_persona(ship* shipp) {
 			return i;
 		}
 	}
-	int count = (int)candidates.size();
-	if (count == 0) {
-		return -1;
-	} else if (count == 1) {
+	int count = (int) candidates.size();
+	if (count == 1) {
 		return candidates[0];
-	} else {
+	} else if (count > 1) {
 		return candidates[Random::next(0, count)];
-	}
+	} else if (persona_type & PERSONA_FLAG_SUPPORT) {
+		// Species without a support persona (e.g. the UEF) historically used the
+		// first support persona; retain that behavior
+		return Default_support_persona;
+	} else {
+		return -1;
+	} 
 }
 
 bool can_auto_assign_persona(ship* shipp) {