Sound: readWAV: avoid common exceptions.

Avoid exceptions for the common ‘file not found’ case, and instead
return false / nullptr. Erik says it’s fine.

simgear/sound/readwav.cxx

@@ -380,7 +380,8 @@ namespace simgear
 ALvoid* loadWAVFromFile(const SGPath& path, unsigned int& format, ALsizei& size, ALfloat& freqf, unsigned int& block_align)
 {
   if (!path.exists()) {
-    throw sg_io_exception("loadWAVFromFile: file not found", path);
+    SG_LOG(SG_IO, SG_DEV_ALERT, "loadWAVFromFile: file not found:" << path);
+    return nullptr;
   }
 
   Buffer b;
@@ -395,13 +396,15 @@ ALvoid* loadWAVFromFile(const SGPath& path, unsigned int& format, ALsizei& size,
   fd = gzopen(ps.c_str(), "rb");
 #endif
   if (!fd) {
-    throw sg_io_exception("loadWAVFromFile: unable to open file", path);
+    SG_LOG(SG_IO, SG_DEV_ALERT, "loadWAVFromFile: unable to open file:" << path);
+    return nullptr;
   }
 
   try {
       loadWavFile(fd, &b);
   } catch (sg_exception& e) {
-      throw sg_io_exception(e.getFormattedMessage() + "\nfor: " + path.str());
+      SG_LOG(SG_IO, SG_DEV_ALERT, "loadWAVFromFile:" << e.getFormattedMessage() << "\nfor: " << path);
+      return nullptr;
   }
 
   ALvoid* data = b.data;

simgear/sound/soundmgr_openal.cxx

@@ -813,13 +813,14 @@ bool SGSoundMgr::load( const std::string &samplepath,
 
     auto data = simgear::loadWAVFromFile(samplepath, format, size, freqf, blocksz);
     freq = (ALsizei)freqf;
-    if (data == nullptr) {
+    if (!data) {
-        throw sg_io_exception("Failed to load wav file", sg_location(samplepath));
+        return false;
     }
 
     if (format == AL_FORMAT_STEREO8 || format == AL_FORMAT_STEREO16) {
          free(data);
-        throw sg_io_exception("Warning: STEREO files are not supported for 3D audio effects: " + samplepath);
+        SG_LOG(SG_IO, SG_DEV_ALERT, "Warning: STEREO files are not supported for 3D audio effects: " << samplepath);
+        return false;
     }
 
     *dbuf = (void *)data;