Added a '-' so that CM_EXTRAVERSION isn't squished into the device name

Patch 2: Fixed the possibility of no CM_EXTRAVERSION resulting in 2 '-' at the end of the file name.

Change-Id: I3025977a5da1e28247c74416e1ac50fc6901eb23
diff --git a/config/common.mk b/config/common.mk
index 39e773e..d183a85 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -124,6 +124,9 @@
     CM_VERSION :=$(PRODUCT_VERSION_MAJOR)-$(shell date +%Y%m%d)-NIGHTLY-$(CM_BUILD)
 else
     ifdef CM_SNAPSHOT
+        ifdef CM_EXTRAVERSION
+            CM_EXTRAVERSION := -$(CM_EXTRAVERSION)
+        endif
         CM_VERSION := $(PRODUCT_VERSION_MAJOR)-$(shell date +%Y%m%d)-SNAPSHOT-$(CM_BUILD)$(CM_EXTRAVERSION)
     else
         ifdef CM_RELEASE