GB Memory: Prevent accessing empty SRAM (fixes #831)

CHANGES

@@ -9,6 +9,7 @@ Bugfixes:
  - GB Video: Fix 16-bit screenshots (fixes mgba.io/i/826)
  - GB Core: Fix palette loading when loading a foreign config
  - Qt: Fix LOG argument order
+ - GB Memory: Prevent accessing empty SRAM (fixes mgba.io/i/831)
 Misc:
  - Qt: Don't rebuild library view if style hasn't changed
 

src/gb/memory.c

@@ -220,7 +220,7 @@ uint8_t GBLoad8(struct LR35902Core* cpu, uint16_t address) {
 			return memory->rtcRegs[memory->activeRtcReg];
 		} else if (memory->mbcRead) {
 			return memory->mbcRead(memory, address);
-		} else if (memory->sramAccess) {
+		} else if (memory->sramAccess && memory->sram) {
 			return memory->sramBank[address & (GB_SIZE_EXTERNAL_RAM - 1)];
 		} else if (memory->mbcType == GB_HuC3) {
 			return 0x01; // TODO: Is this supposed to be the current SRAM bank?
@@ -289,7 +289,7 @@ void GBStore8(struct LR35902Core* cpu, uint16_t address, int8_t value) {
 	case GB_REGION_EXTERNAL_RAM + 1:
 		if (memory->rtcAccess) {
 			memory->rtcRegs[memory->activeRtcReg] = value;
-		} else if (memory->sramAccess) {
+		} else if (memory->sramAccess && memory->sram) {
 			memory->sramBank[address & (GB_SIZE_EXTERNAL_RAM - 1)] = value;
 		} else if (memory->mbcType == GB_MBC7) {
 			GBMBC7Write(memory, address, value);
@@ -387,7 +387,7 @@ uint8_t GBView8(struct LR35902Core* cpu, uint16_t address, int segment) {
 		if (memory->rtcAccess) {
 			return memory->rtcRegs[memory->activeRtcReg];
 		} else if (memory->sramAccess) {
-			if (segment < 0) {
+			if (segment < 0 && memory->sram) {
 				return memory->sramBank[address & (GB_SIZE_EXTERNAL_RAM - 1)];
 			} else if ((size_t) segment * GB_SIZE_EXTERNAL_RAM < gb->sramSize) {
 				return memory->sram[(address & (GB_SIZE_EXTERNAL_RAM - 1)) + segment *GB_SIZE_EXTERNAL_RAM];