Fix a security issue in FPDF_GetMetaText
Fix a security issue in FPDF_GetMetaText

BUG=security

Review URL: https://codereview.chromium.org/307653002

coolwanglu/PDFium.js,azunite/pdfium_ch,aschepis/pdfium,wwxxyx/pdfium0,pwaller/pdfium,nathanstitt/pdfium,rouault/pdfium,PDFium/PDFium,duanhjlt/pdfium,klokantech/pdfium,andoma/pdfium,csharpengineer/pdfium-code,csharpengineer/pdfium-code,was4444/pdfium,hunslater/pdfium,andoma/pdfium,azunite/pdf_clone,codemonkey85/pdfium,aschepis/pdfium,azunite/pdf_clone,witwall/pdfium,azunite/libpdfium,azunite/pdfium_ch,DrAlexx/pdfium,wwxxyx/pdfium0,was4444/pdfium,andoma/pdfium,chenjian-rits/HelloWorld,ttyangf/PDFium-,azunite/pdfium_ch,shifucun/pdfium,bradh/pdfium,was4444/pdfium,rouault/pdfium,Gottox/pdfium,Gottox/pdfium,hunslater/pdfium,witwall/pdfium,PDFium/PDFium,bradh/pdfium,csharpengineer/pdfium-code,coolwanglu/PDFium.js,PDFium/PDFium,duanhjlt/pdfium,duanhjlt/pdfium,wwxxyx/pdfium0,klokantech/pdfium,DrAlexx/pdfium,pwaller/pdfium,hunslater/pdfium,rouault/pdfium,andoma/pdfium,azunite/libpdfium,coolwanglu/PDFium.js,DrAlexx/pdfium,azunite/pdf_clone,chenjian-rits/HelloWorld,shifucun/pdfium,ttyangf/PDFium-,klokantech/pdfium,coolwanglu/PDFium.js,coolwanglu/PDFium.js,pwaller/pdfium,codemonkey85/pdfium,chenjian-rits/HelloWorld,ttyangf/PDFium-,shifucun/pdfium,Gottox/pdfium,was4444/pdfium,aschepis/pdfium,nathanstitt/pdfium,azunite/libpdfium,nathanstitt/pdfium,codemonkey85/pdfium,bradh/pdfium,duanhjlt/pdfium,azunite/libpdfium,witwall/pdfium,DrAlexx/pdfium