Only consider a read successful when the file seems valid

Require at least the `fields` entry to be present,
so we can have a decent guess that it was indeed a settings file.

Settings.c

@@ -172,7 +172,8 @@ static bool Settings_read(Settings* this, const char* fileName) {
    if (!fd)
       return false;
    
-   bool readMeters = false;
+   bool didReadMeters = false;
+   bool didReadFields = false;
    for (;;) {
       char* line = String_readLine(fd);
       if (!line) {
@@ -187,6 +188,7 @@ static bool Settings_read(Settings* this, const char* fileName) {
       }
       if (String_eq(option[0], "fields")) {
          readFields(this->fields, &(this->flags), option[1]);
+         didReadFields = true;
       } else if (String_eq(option[0], "sort_key")) {
          // This "+1" is for compatibility with the older enum format.
          this->sortKey = atoi(option[1]) + 1;
@@ -232,24 +234,24 @@ static bool Settings_read(Settings* this, const char* fileName) {
          if (this->colorScheme < 0 || this->colorScheme >= LAST_COLORSCHEME) this->colorScheme = 0;
       } else if (String_eq(option[0], "left_meters")) {
          Settings_readMeters(this, option[1], 0);
-         readMeters = true;
+         didReadMeters = true;
       } else if (String_eq(option[0], "right_meters")) {
          Settings_readMeters(this, option[1], 1);
-         readMeters = true;
+         didReadMeters = true;
       } else if (String_eq(option[0], "left_meter_modes")) {
          Settings_readMeterModes(this, option[1], 0);
-         readMeters = true;
+         didReadMeters = true;
       } else if (String_eq(option[0], "right_meter_modes")) {
          Settings_readMeterModes(this, option[1], 1);
-         readMeters = true;
+         didReadMeters = true;
       }
       String_freeArray(option);
    }
    fclose(fd);
-   if (!readMeters) {
+   if (!didReadMeters) {
       Settings_defaultMeters(this);
    }
-   return true;
+   return didReadFields;
 }
 
 static void writeFields(FILE* fd, ProcessField* fields, const char* name) {