Revert "Remove unnecessary return"

This reverts commit 3053ded760a9657bdc7b935beb61d2f632859928.
diff --git a/system/database/drivers/pdo/subdrivers/pdo_firebird_driver.php b/system/database/drivers/pdo/subdrivers/pdo_firebird_driver.php
index bb2e282..3bd5c93 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_firebird_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_firebird_driver.php
@@ -120,7 +120,7 @@
 
 		if ($prefix_limit === TRUE && $this->dbprefix !== '')
 		{
-			$sql .' AND "RDB$RELATION_NAME" LIKE \''.$this->escape_like_str($this->dbprefix)."%' "
+			return $sql.' AND "RDB$RELATION_NAME" LIKE \''.$this->escape_like_str($this->dbprefix)."%' "
 				.sprintf($this->_like_escape_str, $this->_like_escape_chr);
 		}
 
diff --git a/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php b/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php
index 8065b36..67dc5f5 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php
@@ -170,7 +170,7 @@
 
 		if ($prefix_limit === TRUE && $this->dbprefix !== '')
 		{
-			$sql ." LIKE '".$this->escape_like_str($this->dbprefix)."%'";
+			return $sql." LIKE '".$this->escape_like_str($this->dbprefix)."%'";
 		}
 
 		return $sql;
diff --git a/system/database/drivers/pdo/subdrivers/pdo_oci_driver.php b/system/database/drivers/pdo/subdrivers/pdo_oci_driver.php
index c85a4a2..d17e311 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_oci_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_oci_driver.php
@@ -143,7 +143,7 @@
 
 		if ($prefix_limit === TRUE && $this->dbprefix !== '')
 		{
-			$sql .' WHERE "TABLE_NAME" LIKE \''.$this->escape_like_str($this->dbprefix)."%' "
+			return $sql.' WHERE "TABLE_NAME" LIKE \''.$this->escape_like_str($this->dbprefix)."%' "
 				.sprintf($this->_like_escape_str, $this->_like_escape_chr);
 		}
 
diff --git a/system/database/drivers/pdo/subdrivers/pdo_odbc_driver.php b/system/database/drivers/pdo/subdrivers/pdo_odbc_driver.php
index ab471d6..51c70b6 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_odbc_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_odbc_driver.php
@@ -174,7 +174,7 @@
 
 		if ($prefix_limit !== FALSE && $this->dbprefix !== '')
 		{
-			$sql ." AND table_name LIKE '".$this->escape_like_str($this->dbprefix)."%' "
+			return $sql." AND table_name LIKE '".$this->escape_like_str($this->dbprefix)."%' "
 				.sprintf($this->_like_escape_str, $this->_like_escape_chr);
 		}
 
diff --git a/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php b/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php
index 11decab..2dd41ca 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php
@@ -228,7 +228,7 @@
 
 		if ($prefix_limit === TRUE && $this->dbprefix !== '')
 		{
-			$sql .' AND "table_name" LIKE \''
+			return $sql.' AND "table_name" LIKE \''
 				.$this->escape_like_str($this->dbprefix)."%' "
 				.sprintf($this->_like_escape_str, $this->_like_escape_chr);
 		}
diff --git a/system/database/drivers/pdo/subdrivers/pdo_sqlite_driver.php b/system/database/drivers/pdo/subdrivers/pdo_sqlite_driver.php
index e25bec0..f07f49f 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_sqlite_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_sqlite_driver.php
@@ -111,7 +111,7 @@
 
 		if ($prefix_limit === TRUE && $this->dbprefix !== '')
 		{
-			$sql .' AND "NAME" LIKE \''.$this->escape_like_str($this->dbprefix)."%' "
+			return $sql.' AND "NAME" LIKE \''.$this->escape_like_str($this->dbprefix)."%' "
 				.sprintf($this->_like_escape_str, $this->_like_escape_chr);
 		}