Fix String::split_ crash on empty string.

(cherry picked from commit eb6dedf30f8f571a4eb88889a6de90729906274d)

core/string/ustring.cpp

@@ -1195,6 +1195,9 @@ Vector<double> String::split_floats(const String &p_splitter, bool p_allow_empty
 	Vector<double> ret;
 	int from = 0;
 	int len = length();
+	if (len == 0) {
+		return ret;
+	}
 
 	String buffer = *this;
 	while (true) {
@@ -1222,6 +1225,9 @@ Vector<float> String::split_floats_mk(const Vector<String> &p_splitters, bool p_
 	Vector<float> ret;
 	int from = 0;
 	int len = length();
+	if (len == 0) {
+		return ret;
+	}
 
 	String buffer = *this;
 	while (true) {
@@ -1254,6 +1260,9 @@ Vector<int> String::split_ints(const String &p_splitter, bool p_allow_empty) con
 	Vector<int> ret;
 	int from = 0;
 	int len = length();
+	if (len == 0) {
+		return ret;
+	}
 
 	while (true) {
 		int end = find(p_splitter, from);
@@ -1278,6 +1287,9 @@ Vector<int> String::split_ints_mk(const Vector<String> &p_splitters, bool p_allo
 	Vector<int> ret;
 	int from = 0;
 	int len = length();
+	if (len == 0) {
+		return ret;
+	}
 
 	while (true) {
 		int idx = 0;