Merge pull request #50 from advmach/gcc-10-warning-fix

Fix 3 compilation warnings with GCC 10 when using -Og optimization (-Og is for easier debugging) 
diff --git a/src/qcbor_decode.c b/src/qcbor_decode.c
index 7d40026..e1820b9 100644
--- a/src/qcbor_decode.c
+++ b/src/qcbor_decode.c
@@ -715,9 +715,9 @@
     an encoding of the length of the uNumber and is needed to decode
     floats and doubles
    */
-   int      nMajorType;
-   uint64_t uNumber;
-   int      nAdditionalInfo;
+   int      nMajorType = 0;
+   uint64_t uNumber = 0;
+   int      nAdditionalInfo = 0;
 
    memset(pDecodedItem, 0, sizeof(QCBORItem));