Assert valid CS

The coding scheme converted to number make sense only if it's
valid. This is implicitly assumed by the code using this conversion as
non-zero value. Make those assumptions explicit with OSMO_ASSERT().

Change-Id: I8f62627b7b7b89dfa1b0d1a7e71b95b2c40fdffa
Fixes: CID70466

src/gprs_coding_scheme.h

@@ -23,6 +23,9 @@
 #include <stdint.h>
 #include <stddef.h>
 
+extern "C" {
+	#include <osmocom/core/utils.h>
+}
 
 class GprsCodingScheme {
 public:
@@ -236,6 +239,9 @@ inline GprsCodingScheme::Scheme GprsCodingScheme::get_retx_mcs(
 				const GprsCodingScheme demanded_mcs,
 				const unsigned arq_type)
 {
+	OSMO_ASSERT(mcs.to_num() > 0);
+	OSMO_ASSERT(demanded_mcs.to_num() > 0);
+
 	return egprs_mcs_retx_tbl[arq_type][mcs.to_num() - 1]
 			[demanded_mcs.to_num() - 1];
 }

src/gprs_ms.cpp

@@ -630,6 +630,8 @@ void GprsMs::update_cs_ul(const pcu_l1_meas *meas)
 		return;
 	}
 
+	OSMO_ASSERT(current_cs_num > 0);
+
 	if (!m_current_cs_ul)
 		return;