Fix usuarios module: resolve PHP 8 warnings and fatal errors

- Fixed undefined array key warnings in usuarios-agregar.php
- Fixed undefined variable warnings (, , )
- Fixed null array offset warnings in db.class.php GetSingle()
- Added default parameter to ValidateMail() in util.class.php
- Fixed PrintErrors() return value for proper error handling
- Fixed integer constraint errors for codigoPostal and sucursalId
- Added missing identificacion and comprobante fields to INSERT query
- Fixed undefined  variable in IsEmailTaked()

classes/util.class.php

@@ -168,15 +168,15 @@ class Util extends SystemError
 			return true;
 		}
 	}//ValidateFloat
-	
-	function ValidateMail($mail, $field)
+
+	function ValidateMail($mail, $field = 'Email')
 	{
 		$mail = strtolower($mail);
 		if (!preg_match('/^[_a-zA-Z0-9-]+(\.[_a-zA-Z0-9-]+)*@[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)+$/',trim($mail)))
 		{
 			return $this->setError(10002, "error", "", $field);
 		}
-	}	
+	}
 
 	function ValidateUrl($url)
 	{
@@ -477,12 +477,16 @@ class Util extends SystemError
 	
 	function PrintErrors()
 	{
+		if(empty($this->error)){
+			return false;
+		}
+
 		$errorStr = "<div id='error-box'>";
 		foreach($this->error as $key => $val)
 		{
 			$msg = $this->errorMessage($val);
-			$field = $this->errorField[$key];
-			
+			$field = isset($this->errorField[$key]) ? $this->errorField[$key] : '';
+
 			$errorStr .= "<div class='error-item'>";
 			if($field != "")
 			{
@@ -493,6 +497,7 @@ class Util extends SystemError
 		}
 		$errorStr .= "</div>";
 		echo $errorStr;
+		return true;
 	}
 	
 	function errorMessage($code)