Clean EXIF data extracted from images

When extracting EXIF data from images some garbage string containing U+0000 characters may be returned, and these will fail to be saved to PostgreSQL.

Caused by: org.nuxeo.ecm.core.storage.StorageException: Could not insert: INSERT INTO "image_metadata" ("id", "icc_profile", "white_balance", "pixel_xdimension", "yresolution", "copyright", "color_space", "date_time_original", "orientation", "xresolution", "user_comment", "image_description", "pixel_ydimension", "iso_speed_ratings", "equipment", "fnumber", "focal_length", "exposure_time") VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?) at org.nuxeo.ecm.core.storage.sql.jdbc.JDBCRowMapper.insertSimpleRows(JDBCRowMapper.java:606) ...
Caused by: java.sql.BatchUpdateException: Batch entry 0 INSERT INTO "image_metadata" ("id", "icc_profile", "white_balance", "pixel_xdimension", "yresolution", "copyright", "color_space", "date_time_original", "orientation", "xresolution", "user_comment", "image_description", "pixel_ydimension", "iso_speed_ratings", "equipment", "fnumber", "focal_length", "exposure_time") VALUES ('c85a74b1-f253-441e-bdcf-d440a2aef14f', NULL, 'auto', 3264, 72, NULL, 'SRGB', '2014-01-31 10:43:44.000000 +01:00:00', 'TOP_LEFT', 72, 'KJKJAKJKJA�ecuteBatch(AbstractJdbc2Statement.java:2893) at org.apache.tomcat.dbcp.dbcp.DelegatingStatement.executeBatch(DelegatingStatement.java:297) at org.apache.tomcat.dbcp.dbcp.DelegatingStatement.executeBatch(DelegatingStatement.java:297) at org.nuxeo.ecm.core.storage.sql.jdbc.JDBCRowMapper.insertSimpleRows(JDBCRowMapper.java:590) ... 20 more
Caused by: org.postgresql.util.PSQLException: ERROR: invalid byte sequence for encoding "UTF8": 0x00 at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2157) at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1886) ... 25 more