GChecksum: accept NULL pointer with length 0
GChecksum: accept NULL pointer with length 0

Several GChecksum functions were incorrectly aborting when passed a NULL
data pointer, even if the length parameter was equal to zero.

lukasz-skalski/glib,pstglia/external-bluetooth-glib,tchakabam/glib,MathieuDuponchelle/glib,bluez-android/glib,mzabaluev/glib,krichter722/glib,pstglia/platform-external-bluetooth-glib,endlessm/glib,tchakabam/glib,antono/glib,djdeath/glib,lukasz-skalski/glib,cosimoc/glib,johne53/MB3Glib,zsx/glib,cosimoc/glib,mzabaluev/glib,ahmedammar/platform_external_gst_glib,tchakabam/glib,bratsche/glib,darren-clark/android_platform_external_bluetooth_glib,johne53/MB3Glib,endlessm/glib,tamaskenez/glib,zsx/glib,ieei/glib,darren-clark/android_platform_external_bluetooth_glib,pstglia/external-bluetooth-glib,cosimoc/glib,MathieuDuponchelle/glib,krichter722/glib,krichter722/glib,gale320/glib,ieei/glib-old-android,tamaskenez/glib,ieei/glib-old-android,mzabaluev/glib,Distrotech/glib,johne53/MB3Glib,tamaskenez/glib,gale320/glib,antono/glib,iConsole/Console-OS_external_bluetooth_glib,Distrotech/glib,iConsole/Console-OS_external_bluetooth_glib,bluez-android/glib,gale320/glib,ahmedammar/platform_external_gst_glib,cention-sany/glib,johne53/MB3Glib,tamaskenez/glib,bratsche/glib,dicer/android_external_glib,lukasz-skalski/glib,lukasz-skalski/glib,bluez-android/glib,endlessm/glib,cention-sany/glib,bratsche/glib,mzabaluev/glib,01org/android-bluez-glib,justinkb/aosp-bluez.glib,bratsche/glib,antono/glib,ieei/glib-old-android,pstglia/platform-external-bluetooth-glib,Distrotech/glib,Distrotech/glib,cention-sany/glib,dicer/android_external_glib,mzabaluev/glib,djdeath/glib,pstglia/platform-external-bluetooth-glib,endlessm/glib,ahmedammar/platform_external_gst_glib,01org/android-bluez-glib,MathieuDuponchelle/glib,krichter722/glib,ieei/glib-old-android,pstglia/external-bluetooth-glib,johne53/MB3Glib,justinkb/aosp-bluez.glib,lukasz-skalski/glib,gale320/glib,pstglia/external-bluetooth-glib,iConsole/Console-OS_external_bluetooth_glib,iConsole/Console-OS_external_bluetooth_glib,cention-sany/glib,darren-clark/android_platform_external_bluetooth_glib,pstglia/platform-external-bluetooth-glib,ieei/glib,ieei/glib,djdeath/glib,zsx/glib,cention-sany/glib,cosimoc/glib,gale320/glib,ieei/glib,tchakabam/glib,MathieuDuponchelle/glib,MathieuDuponchelle/glib,Distrotech/glib,zsx/glib,antono/glib,01org/android-bluez-glib,tamaskenez/glib,01org/android-bluez-glib,pstglia/external-bluetooth-glib,krichter722/glib,iConsole/Console-OS_external_bluetooth_glib,justinkb/aosp-bluez.glib,bluez-android/glib,endlessm/glib,tchakabam/glib,djdeath/glib,djdeath/glib,johne53/MB3Glib,darren-clark/android_platform_external_bluetooth_glib,dicer/android_external_glib,dicer/android_external_glib,ahmedammar/platform_external_gst_glib,01org/android-bluez-glib,dicer/android_external_glib,bluez-android/glib,cosimoc/glib,justinkb/aosp-bluez.glib,ieei/glib,justinkb/aosp-bluez.glib,darren-clark/android_platform_external_bluetooth_glib,pstglia/platform-external-bluetooth-glib