Adjusted check to remove prereqs from skill_tree

* Fixes #1973.
* Setting a prerequisite skill to 0 will now remove it rather than skip it in the skill_tree import.
Thanks to @KrokusPokus!

src/map/pc.c

@@ -10699,15 +10699,15 @@ static bool pc_readdb_skilltree(char* fields[], int columns, int current)
 		return false;
 	}
 	if (skill_lv > (skill_lv_max = skill_get_max(skill_id))) {
-		ShowWarning("pc_readdb_skilltree: Skill %hu's level %hu exceeds job %d's max level %hu. Capping skill level..\n", skill_id, skill_lv, class_, skill_lv_max);
+		ShowWarning("pc_readdb_skilltree: Skill %hu's level %hu exceeds job %d's max level %hu. Capping skill level.\n", skill_id, skill_lv, class_, skill_lv_max);
 		skill_lv = skill_lv_max;
 	}
 	if (baselv > (baselv_max = pc_class_maxbaselv(class_))) {
-		ShowWarning("pc_readdb_skilltree: Skill %hu's base level requirement %d exceeds job %d's max base level %d. Capping skill base level..\n", skill_id, baselv, class_, baselv_max);
+		ShowWarning("pc_readdb_skilltree: Skill %hu's base level requirement %d exceeds job %d's max base level %d. Capping skill base level.\n", skill_id, baselv, class_, baselv_max);
 		baselv = baselv_max;
 	}
 	if (joblv > (joblv_max = pc_class_maxjoblv(class_))) {
-		ShowWarning("pc_readdb_skilltree: Skill %hu's job level requirement %d exceeds job %d's max job level %d. Capping skill job level..\n", skill_id, joblv, class_, joblv_max);
+		ShowWarning("pc_readdb_skilltree: Skill %hu's job level requirement %d exceeds job %d's max job level %d. Capping skill job level.\n", skill_id, joblv, class_, joblv_max);
 		joblv = joblv_max;
 	}
 
@@ -10733,14 +10733,19 @@ static bool pc_readdb_skilltree(char* fields[], int columns, int current)
 		skill_id = (uint16)atoi(fields[i * 2 + offset]);
 		skill_lv = (uint16)atoi(fields[i * 2 + offset + 1]);
 
-		if (skill_id == 0)
+		if (skill_id == 0) {
+			if (skill_tree[idx][skill_idx].need[i].skill_id > 0) { // Remove pre-requisite
+				skill_tree[idx][skill_idx].need[i].skill_id = 0;
+				skill_tree[idx][skill_idx].need[i].skill_lv = 0;
+			}
 			continue;
+		}
 		if (skill_id > MAX_SKILL_ID || !skill_get_index(skill_id)) {
 			ShowWarning("pc_readdb_skilltree: Unable to load requirement skill %hu into job %d's tree.", skill_id, class_);
 			return false;
 		}
 		if (skill_lv > (skill_lv_max = skill_get_max(skill_id))) {
-			ShowWarning("pc_readdb_skilltree: Skill %hu's level %hu exceeds job %d's max level %hu. Capping skill level..\n", skill_id, skill_lv, class_, skill_lv_max);
+			ShowWarning("pc_readdb_skilltree: Skill %hu's level %hu exceeds job %d's max level %hu. Capping skill level.\n", skill_id, skill_lv, class_, skill_lv_max);
 			skill_lv = skill_lv_max;
 		}